mm: pagewalk: fix the comment for test_walk

Modify the comment describing struct mm_walk->test_walk()s behaviour to
match the comment on walk_page_test() and the behaviour of
walk_page_vma().

Fixes: fafaa4264eba4 ("pagewalk: improve vma handling")
Link: http://lkml.kernel.org/r/1471622518-21980-1-git-send-email-james.morse@arm.com
Signed-off-by: James Morse <james.morse@arm.com>
Cc: 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>

include/linux/mm.h

@@ -1197,10 +1197,10 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
  * @pte_hole: if set, called for each hole at all levels
  * @hugetlb_entry: if set, called for each hugetlb entry
  * @test_walk: caller specific callback function to determine whether
- *             we walk over the current vma or not. A positive returned
+ *             we walk over the current vma or not. Returning 0
  *             value means "do page table walk over the current vma,"
  *             and a negative one means "abort current page table walk
- *             right now." 0 means "skip the current vma."
+ *             right now." 1 means "skip the current vma."
  * @mm:        mm_struct representing the target process of page table walk
  * @vma:       vma currently walked (NULL if walking outside vmas)
  * @private:   private data for callbacks' usage