mm/memory-failure.c: use page_shift() in add_to_kill()

page_shift() is supported after the commit 94ad9338 ("mm: introduce
page_shift()").

So replace with page_shift() in add_to_kill() for readability.

Link: http://lkml.kernel.org/r/543d8bc9-f2e7-3023-7c35-2e7ed67c0e82@huawei.comSigned-off-by: Yunfeng Ye <yeyunfeng@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-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>

mm/memory-failure.c

@@ -320,7 +320,7 @@ static void add_to_kill(struct task_struct *tsk, struct page *p,
 	if (is_zone_device_page(p))
 		tk->size_shift = dev_pagemap_mapping_shift(p, vma);
 	else
-		tk->size_shift = compound_order(compound_head(p)) + PAGE_SHIFT;
+		tk->size_shift = page_shift(compound_head(p));
 
 	/*
 	 * Send SIGKILL if "tk->addr == -EFAULT". Also, as