x86: kmalloc + memset conversion to kzalloc

arch/x86_64/kernel/io_apic.c | 56080 -> 56038 (-42 bytes)

also eliminate unnecessary local variable assignment.

[ tglx: arch/x86 adaptation ]

Signed-off-by: Mariusz Kozlowski <m.kozlowski@tuxland.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>