PCI: add pci_try_set_mwi

As suggested by Andrew, add pci_try_set_mwi(), which does not require
return-value checking.

- add pci_try_set_mwi() without __must_check
- make it return 0 on success, errno if the "try" failed or error
- review callers

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/net/wireless/prism54/islpci_hotplug.c

@@ -166,8 +166,7 @@ prism54_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	pci_set_master(pdev);
 
 	/* enable MWI */
-	if (!pci_set_mwi(pdev))
-		printk(KERN_INFO "%s: pci_set_mwi(pdev) succeeded\n", DRV_NAME);
+	pci_try_set_mwi(pdev);
 
 	/* setup the network device interface and its structure */
 	if (!(ndev = islpci_setup(pdev))) {