ble_hid_device_demo: fix build if building with c++

Signed-off-by: Elvis Dukaj <elvis.dukaj@gmail.com>
Signed-off-by: liminyang <liminyang@example.com>

Merges https://github.com/espressif/esp-idf/pull/5191

examples/bluetooth/ble_hid_device_demo/main/hid_dev.h

@@ -253,5 +253,9 @@ void hid_keyboard_build_report(uint8_t *buffer, keyboard_cmd_t cmd);
 
 void hid_mouse_build_report(uint8_t *buffer, mouse_cmd_t cmd);
 
+#ifdef __cplusplus
+} // extern "C"
+#endif
+
 #endif /* HID_DEV_H__ */