drm/vc4: remove unused function

Fix the following clang warning:

drivers/gpu/drm/vc4/vc4_vec.c:201:1: warning: unused function
'to_vc4_vec_connector' [-Wunused-function].
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/1618476325-112629-1-git-send-email-jiapeng.chong@linux.alibaba.com

drivers/gpu/drm/vc4/vc4_vec.c

@@ -197,12 +197,6 @@ struct vc4_vec_connector {
 	struct drm_encoder *encoder;
 };
 
-static inline struct vc4_vec_connector *
-to_vc4_vec_connector(struct drm_connector *connector)
-{
-	return container_of(connector, struct vc4_vec_connector, base);
-}
-
 enum vc4_vec_tv_mode_id {
 	VC4_VEC_TV_MODE_NTSC,
 	VC4_VEC_TV_MODE_NTSC_J,