mm/migration: use helper function vma_lookup() in add_page_for_migration

We could use helper function vma_lookup() to lookup the needed vma to
simplify the code.

Link: https://lkml.kernel.org/r/20220318111709.60311-6-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/migrate.c

@@ -1604,8 +1604,8 @@ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
 
 	mmap_read_lock(mm);
 	err = -EFAULT;
-	vma = find_vma(mm, addr);
-	if (!vma || addr < vma->vm_start || !vma_migratable(vma))
+	vma = vma_lookup(mm, addr);
+	if (!vma || !vma_migratable(vma))
 		goto out;
 
 	/* FOLL_DUMP to ignore special (like zero) pages */