Fix a serious bug I introduced while adding in support for CAM interrupts.
It seems I didn't count my 0's properly when adding the new masks into
icu_vector.s pushing SWI_AST_MASK off the end of the array and screwing
up the indexing for SWI_CLOCK_MASK.

Fix the bug icu_vector.s and also reformat the code in both icu_vector.s and
apic_vector.s so that it will be much harder to make the same mistake in
the future.

Submitted by: Bruce Evans <bde@zeta.org.au>