[DeviceDrivers] Fix compiling issue in MMC/SD.

components/drivers/sdio/mmcsd_core.c

@@ -749,7 +749,8 @@ int rt_mmcsd_core_init(void)
     }
 
     rt_sdio_init();
-}
 
+	return 0;
+}
 INIT_PREV_EXPORT(rt_mmcsd_core_init);