mm/gup.c: fix the comment of return value for populate_vma_page_range()

The return value of populate_vma_page_range() is consistent with
__get_user_pages(), and so is the function comment of return value.
Signed-off-by: Tang Yizhou <tangyizhou@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Link: http://lkml.kernel.org/r/20200720034303.29920-1-tangyizhou@huawei.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/gup.c

@@ -1404,7 +1404,8 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
  *
  * This takes care of mlocking the pages too if VM_LOCKED is set.
  *
- * return 0 on success, negative error code on error.
+ * Return either number of pages pinned in the vma, or a negative error
+ * code on error.
  *
  * vma->vm_mm->mmap_lock must be held.
  *