IPoIB: Don't attempt to release resources on error flow

If the ipoib client info isn't found on the _remove_one callback, we
must not attempt to scan the returned null list.  Found by Coverity.

Signed-off-by: Itai Garbi <igarbi@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>