We recently changed x86 to handle more than 256 IRQs.  Add a check in do_IRQ()
just to make sure that nothing went wrong with that implementation.

[chrisw@sous-sol.org: do x86_64 too]
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Andi Kleen <ak@muc.de>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: "Protasevich, Natalie" <Natalie.Protasevich@UNISYS.com>
Cc: <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>