drm/amd/display: Remove unnecessary NULL check in dcn20_set_input_transfer_func

This commit removes an unnecessary NULL check in the
`dcn20_set_input_transfer_func` function in the `dcn20_hwseq.c` file.
The variable `tf` is assigned the address of
`plane_state->in_transfer_func` unconditionally, so it can never be
`NULL`. Therefore, the check `if (tf == NULL)` is unnecessary and has
been removed.

The plane_state->in_transfer_func itself cannot be NULL because it's a
structure, not a pointer. When we do tf =
&plane_state->in_transfer_func;, we're getting the address of that
structure, which will always be valid as long as plane_state itself is
not NULL.

we've already checked if plane_state is NULL with the line if (dpp_base
== NULL || plane_state == NULL) return false;. So, if the code execution
gets to the point where tf = &plane_state->in_transfer_func; is called,
plane_state is guaranteed to be not NULL, and therefore tf will also not
be NULL.

drivers/gpu/drm/amd/amdgpu/../display/dc/hwss/dcn20/dcn20_hwseq.c
    1094 bool dcn20_set_input_transfer_func(struct dc *dc,
    1095                                 struct pipe_ctx *pipe_ctx,
    1096                                 const struct dc_plane_state *plane_state)
    1097 {
    1098         struct dce_hwseq *hws = dc->hwseq;
    1099         struct dpp *dpp_base = pipe_ctx->plane_res.dpp;
    1100         const struct dc_transfer_func *tf = NULL;
                                                ^^^^^^^^^ This assignment is not necessary now.

    1101         bool result = true;
    1102         bool use_degamma_ram = false;
    1103
    1104         if (dpp_base == NULL || plane_state == NULL)
    1105                 return false;
    1106
    1107         hws->funcs.set_shaper_3dlut(pipe_ctx, plane_state);
    1108         hws->funcs.set_blend_lut(pipe_ctx, plane_state);
    1109
    1110         tf = &plane_state->in_transfer_func;
                 ^^^^^
Before there was an if statement but now tf is assigned unconditionally

    1111
--> 1112         if (tf == NULL) {
                 ^^^^^^^^^^^^^^^^^
so these conditions are impossible.

    1113                 dpp_base->funcs->dpp_set_degamma(dpp_base,
    1114                                 IPP_DEGAMMA_MODE_BYPASS);
    1115                 return true;
    1116         }
    1117
    1118         if (tf->type == TF_TYPE_HWPWL || tf->type == TF_TYPE_DISTRIBUTED_POINTS)
    1119                 use_degamma_ram = true;
    1120
    1121         if (use_degamma_ram == true) {
    1122                 if (tf->type == TF_TYPE_HWPWL)
    1123                         dpp_base->funcs->dpp_program_degamma_pwl(dpp_base,

Fixes the below Smatch static checker warning:
drivers/gpu/drm/amd/amdgpu/../display/dc/hwss/dcn20/dcn20_hwseq.c:1112 dcn20_set_input_transfer_func() warn: address of 'plane_state->in_transfer_func' is non-NULL

Fixes: 285a7054 ("drm/amd/display: Remove plane and stream pointers from dc scratch")
Cc: Wenjing Liu <wenjing.liu@amd.com>
Cc: Tom Chung <chiahsuan.chung@amd.com>
Cc: Alvin Lee <alvin.lee2@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Roman Li <roman.li@amd.com>
Cc: Qingqing Zhuo <Qingqing.Zhuo@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Suggested-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/hwss/dcn20/dcn20_hwseq.c

@@ -1109,12 +1109,6 @@ bool dcn20_set_input_transfer_func(struct dc *dc,
 
 	tf = &plane_state->in_transfer_func;
 
-	if (tf == NULL) {
-		dpp_base->funcs->dpp_set_degamma(dpp_base,
-				IPP_DEGAMMA_MODE_BYPASS);
-		return true;
-	}
-
 	if (tf->type == TF_TYPE_HWPWL || tf->type == TF_TYPE_DISTRIBUTED_POINTS)
 		use_degamma_ram = true;