Set brightness to 100% when using display flash

src/flash.h

@@ -1,5 +1,10 @@
+#include "gio/gio.h"
+
 typedef struct _MPFlash MPFlash;
 
+void mp_flash_gtk_init(GDBusConnection *conn);
+void mp_flash_gtk_clean();
+
 MPFlash *mp_led_flash_from_path(const char *path);
 MPFlash *mp_create_display_flash();
 void mp_flash_free(MPFlash *flash);