RDMA/uverbs: Don't do double free of allocated PD

There is no need to call kfree(pd) because ib_dealloc_pd() internally
frees PD.

Fixes: 21a428a0 ("RDMA: Handle PD allocations by IB/core")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/uverbs_cmd.c

@@ -440,6 +440,7 @@ static int ib_uverbs_alloc_pd(struct uverbs_attr_bundle *attrs)
 
 err_copy:
 	ib_dealloc_pd(pd);
+	pd = NULL;
 err_alloc:
 	kfree(pd);
 err: