[PATCH] fix via586 irq routing for pirq 5

Fix interrupt routing for via 586 bridges.  pirq can be 5 which needs to be
mapped to INTD.  But currently the access functions can handle only pirq
1-4.  this is similar to the other via chipsets where pirq 4 and 5 are both
mapped to INTD.  Fixes bugzilla #7490

Cc: Daniel Paschka <monkey20181@gmx.net>
Cc: Adrian Bunk <bunk@susta.de>
Signed-off-by: Daniel Ritz <daniel.ritz@gmx.ch>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>