Fixed the return value bug in sdcard_port.c

Fixed the return value bug in sdcard_port.c

bsp/stm32/stm32f429-atk-apollo/board/ports/sdcard_port.c

@@ -6,6 +6,7 @@
  * Change Logs:
  * Date           Author       Notes
  * 2018-12-13     balanceTWK   add sdcard port file
+ * 2021-02-18     DavidLin     Fixed the return bug
  */
 
 #include <rtthread.h>
@@ -53,6 +54,7 @@ int stm32_sdcard_mount(void)
     else
     {
         LOG_E("create sd_mount thread err!");
+        return RT_ERROR;
     }
     return RT_EOK;
 }