x86: apic: Convert BUG() to BUG_ON()

This was done using Coccinelle's BUG_ON semantic patch.

Signed-off-by: Daniel Walker <dwalker@fifo99.com>
Cc: Julia Lawall <julia@diku.dk>
LKML-Reference: <1252777220-30796-1-git-send-email-dwalker@fifo99.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>