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/starfire.c b/drivers/net/starfire.c
index 786d4b9..2f69d5c 100644
--- a/drivers/net/starfire.c
+++ b/drivers/net/starfire.c
@@ -740,7 +740,7 @@
 	pci_set_master(pdev);
 
 	/* enable MWI -- it vastly improves Rx performance on sparc64 */
-	pci_set_mwi(pdev);
+	pci_try_set_mwi(pdev);
 
 #ifdef ZEROCOPY
 	/* Starfire can do TCP/UDP checksumming */