nfp: Fix passing zero to 'PTR_ERR'

nfp_cpp_from_nfp6000_pcie() returns ERR_PTR() and never returns
NULL. The NULL test should be removed, also return correct err.
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Link: https://lore.kernel.org/r/20201112145852.6580-1-yuehaibing@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/netronome/nfp/nfp_main.c

@@ -724,10 +724,8 @@ static int nfp_pci_probe(struct pci_dev *pdev,
 	}
 
 	pf->cpp = nfp_cpp_from_nfp6000_pcie(pdev);
-	if (IS_ERR_OR_NULL(pf->cpp)) {
+	if (IS_ERR(pf->cpp)) {
 		err = PTR_ERR(pf->cpp);
-		if (err >= 0)
-			err = -ENOMEM;
 		goto err_disable_msix;
 	}