drm/amd/display: Remove redundant non-zero and overflow check

[Why]
Unsigned int is guaranteed to be >= 0, and read_channel_reply checks for
overflows. read_channel_reply also returns -1 on error, which is what
dc_link_aux_transfer is expected to return on error.

[How]
Remove the if-statement. Return result of read_channel_reply directly.
Signed-off-by: Leo (Sunpeng) Li <sunpeng.li@amd.com>
Reviewed-by: Mikita Lipski <Mikita.Lipski@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_link_ddc.c

@@ -666,13 +666,9 @@ int dc_link_aux_transfer(struct ddc_service *ddc,
 
 	switch (operation_result) {
 	case AUX_CHANNEL_OPERATION_SUCCEEDED:
-		res = returned_bytes;
-
-		if (res <= size && res >= 0)
 		res = aux_engine->funcs->read_channel_reply(aux_engine, size,
 							buffer, reply,
 							&status);
-
 		break;
 	case AUX_CHANNEL_OPERATION_FAILED_HPD_DISCON:
 		res = 0;