x86, ioapic: Get rid of needless check and simplify ioapic_setup_resources()

alloc_bootmem() already panics on allocation failure. There is
no need to check the result.

Also there is a way to unbind global variable from its body and
use it as a parameter which allow us to simplify
ioapic_init_mappings as well -- "for" cycle already uses
nr_ioapics as a conditional variable and there is no need to
check if ioapic_setup_resources was returning NULL again.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <20090824175551.493629148@openvz.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>