cifs: Unlock on errors in cifs_swn_reconnect()

There are three error paths which need to unlock before returning.

Fixes: 121d947d

 ("cifs: Handle witness client move notification")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Samuel Cabrero <scabrero@suse.de>
Signed-off-by: Steve French <stfrench@microsoft.com>