drm/vc4: Fix scaling of uni-planar formats

When using uni-planar formats (like RGB), the scaling parameters are
stored in plane 0, not plane 1.

Fixes: fc04023f ("drm/vc4: Add support for YUV planes.")
Cc: stable@vger.kernel.org
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20180507121303.5610-1-boris.brezillon@bootlin.com

drivers/gpu/drm/vc4/vc4_plane.c

@@ -503,7 +503,7 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
 	 * the scl fields here.
 	 */
 	if (num_planes == 1) {
-		scl0 = vc4_get_scl_field(state, 1);
+		scl0 = vc4_get_scl_field(state, 0);
 		scl1 = scl0;
 	} else {
 		scl0 = vc4_get_scl_field(state, 1);