IB/vmw_pvrdma: Don't leak info from alloc_ucontext

Clear out the user response struct correctly.

Fixes: 29c8d9eb

 ("IB: Add vmw_pvrdma driver")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Adit Ranadive <aditr@vmware.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>