IB/mlx5: Fix memory leak in mlx5_ib_create_srq

The patch fixes the rollback in case of failure in creating SRQ.

Signed-off-by: Moshe Lazer <moshel@mellanox.com>
Signed-off-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>