RDMA/mlx5: Don't leak UARs in case of free fails

The failure in releasing one UAR doesn't mean that we can't continue to
release rest of system pages, so don't return too early.

As part of cleanup, there is no need to print warning if
mlx5_cmd_free_uar() fails because such warning will be printed as part of
mlx5_cmd_exec().

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>