uvch264: fix werror build with clang

uvch264: fix werror build with clang

../subprojects/gst-plugins-bad/sys/uvch264/gstuvch264deviceprovider.c:48:1: warning: unused function 'GST__UVC_H264_DEVICE' [-Wunused-function]
G_DECLARE_FINAL_TYPE (GstUvcH264Device, gst_uvc_h264_device, GST_,
^
/usr/include/glib-2.0/gobject/gtype.h:1405:33: note: expanded from macro 'G_DECLARE_FINAL_TYPE'
  static inline ModuleObjName * MODULE##_##OBJ_NAME (gpointer ptr) {                                     \
                                ^
<scratch space>:75:1: note: expanded from here
GST__UVC_H264_DEVICE
^
../subprojects/gst-plugins-bad/sys/uvch264/gstuvch264deviceprovider.c:48:1: warning: unused function 'GST__IS_UVC_H264_DEVICE' [-Wunused-function]
/usr/include/glib-2.0/gobject/gtype.h:1407:26: note: expanded from macro 'G_DECLARE_FINAL_TYPE'
  static inline gboolean MODULE##_IS_##OBJ_NAME (gpointer ptr) {                                         \
                         ^
<scratch space>:78:1: note: expanded from here
GST__IS_UVC_H264_DEVICE
^
../subprojects/gst-plugins-bad/sys/uvch264/gstuvch264deviceprovider.c:139:1: warning: unused function 'GST_UVC_H264_DEVICE_PROVIDER' [-Wunused-function]
G_DECLARE_FINAL_TYPE (GstUvcH264DeviceProvider, gst_uvc_h264_device_provider, GST, UVC_H264_DEVICE_PROVIDER, GstDeviceProvider)
^
/usr/include/glib-2.0/gobject/gtype.h:1405:33: note: expanded from macro 'G_DECLARE_FINAL_TYPE'
  static inline ModuleObjName * MODULE##_##OBJ_NAME (gpointer ptr) {                                     \
                                ^
<scratch space>:137:1: note: expanded from here
GST_UVC_H264_DEVICE_PROVIDER
^
../subprojects/gst-plugins-bad/sys/uvch264/gstuvch264deviceprovider.c:139:1: warning: unused function 'GST_IS_UVC_H264_DEVICE_PROVIDER' [-Wunused-function]
/usr/include/glib-2.0/gobject/gtype.h:1407:26: note: expanded from macro 'G_DECLARE_FINAL_TYPE'
  static inline gboolean MODULE##_IS_##OBJ_NAME (gpointer ptr) {                                         \
                         ^
<scratch space>:140:1: note: expanded from here
GST_IS_UVC_H264_DEVICE_PROVIDER
^