mm/page_isolation: use macro to judge the alignment

Signed-off-by: Wang Xiaoqiang <wangxq10@lzu.edu.cn>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>