cxl: Fix error handling in _cxl_cx4_setup_msi_irqs()

'cxl_dev_context_init()' returns an error pointer in case of error, not
NULL. So test it with IS_ERR.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Acked-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Acked-by: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

drivers/misc/cxl/api.c

@@ -538,7 +538,7 @@ int _cxl_cx4_setup_msi_irqs(struct pci_dev *pdev, int nvec, int type)
 
 		if (remaining > 0) {
 			new_ctx = cxl_dev_context_init(pdev);
-			if (!new_ctx) {
+			if (IS_ERR(new_ctx)) {
 				pr_warn("%s: Failed to allocate enough contexts for MSIs\n", pci_name(pdev));
 				return -ENOSPC;
 			}