This fixes a bug where, if we try to set the affinity on an unused
virtual IRQ number on a logically-partitioned pSeries system, we call
the firmware with physical IRQ number = -1, which it doesn't like.

With this patch we just ignore the attempt.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>