Add the missing unlock before return from function tile_net_open()
in the error handling case.
Introduced by commit 
f3286a3af89d6db7a488f3e8f02b98d67d50f00c.
(tile: support multiple mPIPE shims in tilegx network driver)
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Chris Metcalf <cmetcalf@tilera.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
 
 
        /* Get the instance info. */
        rc = gxio_mpipe_link_instance(dev->name);
-       if (rc < 0 || rc >= NR_MPIPE_MAX)
+       if (rc < 0 || rc >= NR_MPIPE_MAX) {
+               mutex_unlock(&tile_net_devs_for_channel_mutex);
                return -EIO;
+       }
 
        priv->instance = rc;
        instance = rc;