x86: remove bogus 'pci=usepirqmask' suggestion when no irq is defined

This was harmless, but for the case of a device that had no irq
pre-defined we would incorrectly suggest that "usepirqmask" might make a
difference.  It never would, and the message was just confusing people.

Reported in the dmesg of Etienne Lorrain.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>