CIFS: Fix a memory leak when a lease break comes

This happens when we receive a lease break from a server, then
find an appropriate lease key in opened files and schedule the
oplock_break slow work. lw pointer isn't freed in this case.

Cc: <stable@vger.kernel.org>
Signed-off-by: Pavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>