[PATCH] powerpc: make OF interrupt tree parsing more strict

This patch fixes a bit of boundchecking in the new Open Firmware interrupt
tree parsing code.  It's important that it fails when things aren't correct in
order to trigger fallback mecanisms that are necessary to make some machines
work properly.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>