drm/i915: Disable plane gamma in SKL+ sprite planes

The plane gamma tables are never programmed, so just disable it, like it
is done for the primary plane.

Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1485429865-10687-2-git-send-email-ander.conselvan.de.oliveira@intel.com

drivers/gpu/drm/i915/intel_sprite.c

@@ -226,6 +226,7 @@ skl_update_plane(struct drm_plane *drm_plane,
 	plane_ctl |= skl_plane_ctl_format(fb->format->format);
 	plane_ctl |= skl_plane_ctl_tiling(fb->modifier);
 
+	plane_ctl |= PLANE_CTL_PLANE_GAMMA_DISABLE;
 	plane_ctl |= skl_plane_ctl_rotation(rotation);
 
 	if (key->flags) {