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>