rpicamsrc: deviceprovider: hook up i18n properly

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/merge_requests/682>

po/POTFILES

@@ -20,6 +20,7 @@ sys/oss4/oss4-source.c
 sys/oss/gstosssink.c
 sys/oss/gstosssrc.c
 sys/osxaudio/gstosxaudioringbuffer.c
+sys/rpicamsrc/gstrpicamsrcdeviceprovider.c
 sys/v4l2/gstv4l2bufferpool.c
 sys/v4l2/gstv4l2object.c
 sys/v4l2/gstv4l2radio.c

sys/rpicamsrc/gstrpicamsrcdeviceprovider.c

@@ -27,8 +27,7 @@
 
 #include "RaspiCapture.h"
 
-/* FIXME: translations */
-#define _(s) s
+#include <gst/gst-i18n-plugin.h>
 
 static GstRpiCamSrcDevice *gst_rpi_cam_src_device_new (void);