add support for OFW - declare reverse_mac

applications/system/findmy/findmy_i.h

@@ -20,6 +20,9 @@
 #include <gui/modules/popup.h>
 #include "scenes/findmy_scene.h"
 #include "helpers/base64.h"
+#if FW_ORIGIN_Official
+void furi_hal_bt_reverse_mac_addr(uint8_t mac_addr[GAP_MAC_ADDR_SIZE]);
+#endif
 
 struct FindMy {
     Gui* gui;