drm/amd/display: Fix bug in debugfs crc_win_update entry

[Why]
crc_rd_wrk shouldn't be null in crc_win_update_set(). Current programming
logic is inconsistent in crc_win_update_set().

[How]
Initially, return if crc_rd_wrk is NULL. Later on, we can use member of
crc_rd_wrk safely.
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 9a65df19 ("drm/amd/display: Use PSP TA to read out crc")
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Acked-by: Pavle Kotarac <Pavle.Kotarac@amd.com>
Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c

@@ -2953,10 +2953,13 @@ static int crc_win_update_set(void *data, u64 val)
 	struct amdgpu_device *adev = drm_to_adev(new_crtc->dev);
 	struct crc_rd_work *crc_rd_wrk = adev->dm.crc_rd_wrk;
 
+	if (!crc_rd_wrk)
+		return 0;
+
 	if (val) {
 		spin_lock_irq(&adev_to_drm(adev)->event_lock);
 		spin_lock_irq(&crc_rd_wrk->crc_rd_work_lock);
-		if (crc_rd_wrk && crc_rd_wrk->crtc) {
+		if (crc_rd_wrk->crtc) {
 			old_crtc = crc_rd_wrk->crtc;
 			old_acrtc = to_amdgpu_crtc(old_crtc);
 		}