[bsp] Mini optimized the fh_mmc.c

Deleted the un-reach code line 'break;'

bsp/fh8620/libraries/driverlib/fh_mmc.c

@@ -194,7 +194,6 @@ int MMC_SetCardWidth(struct fh_mmc_obj *mmc_obj, int width)
     default:
         rt_kprintf("ERROR: %s, card width %d is not supported\n", __func__, width);
         return -RT_ERROR;
-        break;
     }
     return 0;
 }