ocfs2: fix memory leak in dlm_migrate_request_handler()

ocfs2: fix memory leak in dlm_migrate_request_handler()

In the dlm_migrate_request_handler(), when `ret' is -EEXIST, the mle
should be freed, otherwise the memory will be leaked.

Link: http://lkml.kernel.org/r/71604351584F6A4EBAE558C676F37CA4A3D3522A@H3CMLB12-EX.srv.huawei-3com.com
Signed-off-by: Guozhonghua <guozhonghua@h3c.com>
Reviewed-by: Mark Fasheh <mfasheh@versity.com>
Cc: Eric Ren <zren@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Joseph Qi <joseph.qi@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>