IB/mlx5: Fix wrong error unwind

The destroy_workqueue on error unwind is missing, and the code jumps to
the wrong exit label.

Fixes: 813e90b1 ("IB/mlx5: Add advise_mr() support")
Acked-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>