free_pd is allocated internally by the driver hence needs to be freed
internally too or it leaks.

Fixes: 21a428a0 ("RDMA: Handle PD allocations by IB/core")
Signed-off-by: NLeon Romanovsky <leonro@mellanox.com>
Acked-by: NLijun Ou <oulijun@huawei.com>
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>