[PATCH] um: irq changes break build

Fixup broken UML build due to 7d12e780
"IRQ: Maintain regs pointer globally rather than passing to IRQ handlers".

Cc: David Howells <dhowells@redhat.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Paolo "Blaisorblade" Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>