RDMA/usnic: Clean up usnic_ib_alloc_pd()

Remove the unnecessary "umem_pd" variable.  And usnic_uiom_alloc_pd()
never returns NULL so remove the NULL check.

Link: https://lore.kernel.org/r/20211118113924.GH1147@kiliSigned-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/hw/usnic/usnic_ib_verbs.c

@@ -442,12 +442,10 @@ int usnic_ib_query_gid(struct ib_device *ibdev, u32 port, int index,
 int usnic_ib_alloc_pd(struct ib_pd *ibpd, struct ib_udata *udata)
 {
 	struct usnic_ib_pd *pd = to_upd(ibpd);
-	void *umem_pd;
 
-	umem_pd = pd->umem_pd = usnic_uiom_alloc_pd();
-	if (IS_ERR_OR_NULL(umem_pd)) {
-		return umem_pd ? PTR_ERR(umem_pd) : -ENOMEM;
-	}
+	pd->umem_pd = usnic_uiom_alloc_pd();
+	if (IS_ERR(pd->umem_pd))
+		return PTR_ERR(pd->umem_pd);
 
 	return 0;
 }