mm: remove unneeded PageAnon check in restore_exclusive_pte()

When code reaches here, the page must be !PageAnon. There's no need to
check PageAnon again. Remove it.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Miaohe Lin <[e-mail]>
Reviewed-by: David Hildenbrand <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

mm/memory.c

···
 		 * Currently device exclusive access only supports anonymous
 		 * memory so the entry shouldn't point to a filebacked page.
 		 */
-		WARN_ON_ONCE(!PageAnon(page));
+		WARN_ON_ONCE(1);
 
 	set_pte_at(vma->vm_mm, address, ptep, pte);