drm/i915: fix accidental static variable use

It's supposed to be just a const pointer.

Fixes: 074c77e3 ("drm/i915/tgl: Gen-12 display loses Yf tiling and legacy CCS support")
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191115120440.17883-1-jani.nikula@intel.com
(cherry picked from commit 48ea97fa)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/display/intel_sprite.c

@@ -2885,7 +2885,7 @@ struct intel_plane *
 skl_universal_plane_create(struct drm_i915_private *dev_priv,
 			   enum pipe pipe, enum plane_id plane_id)
 {
-	static const struct drm_plane_funcs *plane_funcs;
+	const struct drm_plane_funcs *plane_funcs;
 	struct intel_plane *plane;
 	enum drm_plane_type plane_type;
 	unsigned int supported_rotations;