RDMA: Check umem pointer validity prior to release

Update ib_umem_release() to behave similarly to kfree() and allow
submitting NULL pointer as safe input to this function.

Fixes: a52c8e2469 ("RDMA: Clean destroy CQ in drivers do not return errors")
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/core/umem.c

@@ -361,6 +361,9 @@ static void __ib_umem_release_tail(struct ib_umem *umem)
  */
 void ib_umem_release(struct ib_umem *umem)
 {
+	if (!umem)
+		return;
+
 	if (umem->is_odp) {
 		ib_umem_odp_release(to_ib_umem_odp(umem));
 		__ib_umem_release_tail(umem);