drm/amd/display: Avoid overflow from uint32_t to uint8_t

[WHAT & HOW]
dmub_rb_cmd's ramping_boundary has size of uint8_t and it is assigned
0xFFFF. Fix it by changing it to uint8_t with value of 0xFF.

This fixes 2 INTEGER_OVERFLOW issues reported by Coverity.
Reviewed-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dce/dmub_abm_lcd.c

@@ -258,7 +258,7 @@ bool dmub_abm_set_pipe(struct abm *abm,
 {
 	union dmub_rb_cmd cmd;
 	struct dc_context *dc = abm->ctx;
-	uint32_t ramping_boundary = 0xFFFF;
+	uint8_t ramping_boundary = 0xFF;
 
 	memset(&cmd, 0, sizeof(cmd));
 	cmd.abm_set_pipe.header.type = DMUB_CMD__ABM;

drivers/gpu/drm/amd/display/dc/hwss/dcn21/dcn21_hwseq.c

@@ -142,7 +142,7 @@ static bool dmub_abm_set_pipe(struct abm *abm, uint32_t otg_inst,
 {
 	union dmub_rb_cmd cmd;
 	struct dc_context *dc = abm->ctx;
-	uint32_t ramping_boundary = 0xFFFF;
+	uint8_t ramping_boundary = 0xFF;
 
 	memset(&cmd, 0, sizeof(cmd));
 	cmd.abm_set_pipe.header.type = DMUB_CMD__ABM;