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>

diff --git a/drivers/net/cassini.c b/drivers/net/cassini.c
index 805924f..f6e4030 100644
--- a/drivers/net/cassini.c
+++ b/drivers/net/cassini.c
@@ -4917,13 +4917,13 @@
 	pci_cmd &= ~PCI_COMMAND_SERR;
 	pci_cmd |= PCI_COMMAND_PARITY;
 	pci_write_config_word(pdev, PCI_COMMAND, pci_cmd);
-	if (pci_set_mwi(pdev))
+	if (pci_try_set_mwi(pdev))
 		printk(KERN_WARNING PFX "Could not enable MWI for %s\n",
 		       pci_name(pdev));
 
 	/*
 	 * On some architectures, the default cache line size set
-	 * by pci_set_mwi reduces perforamnce.  We have to increase
+	 * by pci_try_set_mwi reduces perforamnce.  We have to increase
 	 * it for this case.  To start, we'll print some configuration
 	 * data.
 	 */