drm/amd/display: Check null-initialized variables

[WHAT & HOW]
drr_timing and subvp_pipe are initialized to null and they are not
always assigned new values. It is necessary to check for null before
dereferencing.

This fixes 2 FORWARD_NULL issues reported by Coverity.
Reviewed-by: Nevenko Stupar <nevenko.stupar@amd.com>
Reviewed-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Jerry Zuo <jerry.zuo@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/dml/dcn32/dcn32_fpu.c

@@ -871,8 +871,9 @@ static bool subvp_drr_schedulable(struct dc *dc, struct dc_state *context)
 	 * for VBLANK: (VACTIVE region of the SubVP pipe can fit the MALL prefetch, VBLANK frame time,
 	 * and the max of (VBLANK blanking time, MALL region)).
 	 */
-	if (stretched_drr_us < (1 / (double)drr_timing->min_refresh_in_uhz) * 1000000 * 1000000 &&
-			subvp_active_us - prefetch_us - stretched_drr_us - max_vblank_mallregion > 0)
+	if (drr_timing &&
+	    stretched_drr_us < (1 / (double)drr_timing->min_refresh_in_uhz) * 1000000 * 1000000 &&
+	    subvp_active_us - prefetch_us - stretched_drr_us - max_vblank_mallregion > 0)
 		schedulable = true;
 
 	return schedulable;
@@ -937,7 +938,7 @@ static bool subvp_vblank_schedulable(struct dc *dc, struct dc_state *context)
 		if (!subvp_pipe && pipe_mall_type == SUBVP_MAIN)
 			subvp_pipe = pipe;
 	}
-	if (found) {
+	if (found && subvp_pipe) {
 		phantom_stream = dc_state_get_paired_subvp_stream(context, subvp_pipe->stream);
 		main_timing = &subvp_pipe->stream->timing;
 		phantom_timing = &phantom_stream->timing;