IB/core: Free umem when mm is already gone

Free umem when task's mm is already destroyed by the time
ib_umem_release gets called.

Found by Dotan Barak at Mellanox.

Signed-off-by: Eli Cohen <eli@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
1 file changed