drm/msm: fix warning "using plain integer as NULL pointer"

Fix sparse warning:
drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c:1195:41: warning: Using plain integer as NULL pointer
drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c:1348:32: warning: Using plain integer as NULL pointer
Signed-off-by: Bernard Zhao <bernard@vivo.com>
Link: https://lore.kernel.org/r/20210510031250.5303-1-bernard@vivo.comSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c

@@ -1193,7 +1193,7 @@ static void dpu_plane_sspp_atomic_update(struct drm_plane *plane)
 		if (DPU_FORMAT_IS_YUV(fmt))
 			_dpu_plane_setup_csc(pdpu);
 		else
-			pdpu->csc_ptr = 0;
+			pdpu->csc_ptr = NULL;
 	}
 
 	_dpu_plane_set_qos_lut(plane, fb);
@@ -1330,7 +1330,7 @@ static void dpu_plane_reset(struct drm_plane *plane)
 	/* remove previous state, if present */
 	if (plane->state) {
 		dpu_plane_destroy_state(plane, plane->state);
-		plane->state = 0;
+		plane->state = NULL;
 	}
 
 	pstate = kzalloc(sizeof(*pstate), GFP_KERNEL);