implemented disk sync()

FATFS/shimatta_sdio_driver/shimatta_sdio-driver.c

@@ -68,8 +68,9 @@ DRESULT SDIO_disk_ioctl(BYTE cmd, void* buff){
         //TODO: Implement
         break;
       case CTRL_SYNC:
-        res = RES_ERROR;
+        res = RES_OK;
-        //TODO: Implement
+        //No cache
+        //Nothing to do
         break;
      default:
         res = RES_PARERR;