RDMA/vmw_pvrdma: Do not re-calculate npages

There is no need to re-calculate the number of pages since it is already
done in ib_umem_get.

Signed-off-by: Yuval Shaia <yuval.shaia@oracle.com>
Acked-by: Adit Ranadive <aditr@vmware.com>
Tested-by: Adit Ranadive <aditr@vmware.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>