RDMA/ocrdma: Fix memory leak in _ocrdma_alloc_pd()

If ocrdma_get_pd_num() fails, then we need to free the pd struct we allocated.

This was detected by Coverity (CID 1271245).

Signed-off-by: Roland Dreier <roland@purestorage.com>
Acked-By: Devesh Sharma <devesh.sharma@avagotech.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>