RDMA/mlx5: Avoid memory leak in case of XRCD dealloc failure

Failure in XRCD FW deallocation command leaves memory leaked and
returns error to the user which he can't do anything about it.

This patch changes behavior to always free memory and always return
success to the user.

Fixes: e126ba97 ("mlx5: Add driver for Mellanox Connect-IB adapters")
Reviewed-by: Majd Dibbiny <majd@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>