mm/hmm: hmm_pfns_bad() was accessing wrong struct

The private field of mm_walk struct point to an hmm_vma_walk struct and
not to the hmm_range struct desired.  Fix to get proper struct pointer.

Link: http://lkml.kernel.org/r/20180323005527.758-6-jglisse@redhat.comSigned-off-by: NJérôme Glisse <jglisse@redhat.com>
Cc: Evgeny Baskakov <ebaskakov@nvidia.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Mark Hairgrove <mhairgrove@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/hmm.c

@@ -336,7 +336,8 @@ static int hmm_pfns_bad(unsigned long addr,
 			unsigned long end,
 			struct mm_walk *walk)
 {
-	struct hmm_range *range = walk->private;
+	struct hmm_vma_walk *hmm_vma_walk = walk->private;
+	struct hmm_range *range = hmm_vma_walk->range;
 	hmm_pfn_t *pfns = range->pfns;
 	unsigned long i;