drm/tilcdc: remove unnecessary state->fb check

tilcdc_plane_atomic_check() exits if state->fb == NULL, so no need to
check it again later.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200429104234.18910-2-tomi.valkeinen@ti.comReviewed-by: Jyri Sarha <jsarha@ti.com>

drivers/gpu/drm/tilcdc/tilcdc_plane.c

@@ -62,8 +62,7 @@ static int tilcdc_plane_atomic_check(struct drm_plane *plane,
 		return -EINVAL;
 	}
 
-	if (state->fb && old_state->fb &&
-	    state->fb->format != old_state->fb->format) {
+	if (old_state->fb && state->fb->format != old_state->fb->format) {
 		dev_dbg(plane->dev->dev,
 			"%s(): pixel format change requires mode_change\n",
 			__func__);