drm/i915: Fix SKL sprite disable double buffer register update

Write the PLANE_SURF register instead of PLANE_CTL to arm the double
buffer regisrter update.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c
index a4c9c66..0f00209 100644
--- a/drivers/gpu/drm/i915/intel_sprite.c
+++ b/drivers/gpu/drm/i915/intel_sprite.c
@@ -301,8 +301,8 @@
 	I915_WRITE(PLANE_CTL(pipe, plane), 0);
 
 	/* Activate double buffered register update */
-	I915_WRITE(PLANE_CTL(pipe, plane), 0);
-	POSTING_READ(PLANE_CTL(pipe, plane));
+	I915_WRITE(PLANE_SURF(pipe, plane), 0);
+	POSTING_READ(PLANE_SURF(pipe, plane));
 
 	intel_update_sprite_watermarks(drm_plane, crtc, 0, 0, 0, false, false);
 }