Fix buffer overrun in sched_getaffinity

Zeroing of the cpu array should start from &cpus[kernel_ret]
not &cpus[num_zeros_to_fill].

This fixes a crash in EFL's edje_cc running under qemu-arm.

Signed-off-by: Mike McCormack <mj.mccormack@samsung.com>
Reviewed-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Acked-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Riku Voipio <riku.voipio@iki.fi>
