Patch from Ben Dooks

_find_first_zero_bit_le and _find_next_zero_bit_le are missing the
const from their pointer arguments, causing the following warnings:
In file included from mm/page_alloc.c:34:
include/linux/nodemask.h: In function `__first_unset_node':
include/linux/nodemask.h:246: warning: passing arg 1 of `_find_first_zero_bit_le' discards qualifiers from pointer target type

Signed-off-by: Ben Dooks
Signed-off-by: Russell King