[PATCH 4.7 056/186] dm verity fec: fix block calculation

4.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sami Tolvanen <samitolvanen@google.com>

commit 602d1657c603eedd7379a8bcde1ad3a2972ecc5f upstream.

do_div was replaced with div64_u64 at some point, causing a bug with
block calculation due to incompatible semantics of the two functions.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Fixes: a739ff3f543a ("dm verity: add support for forward error correction")
Signed-off-by: Mike Snitzer <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/md/dm-verity-fec.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/drivers/md/dm-verity-fec.c
+++ b/drivers/md/dm-verity-fec.c

@@ -453,9 +453,7 @@ int verity_fec_decode(struct dm_verity *
 	 */
 
 	offset = block << v->data_dev_block_bits;
-
-	res = offset;
-	div64_u64(res, v->fec->rounds << v->data_dev_block_bits);
+	res = div64_u64(offset, v->fec->rounds << v->data_dev_block_bits);
 
 	/*
 	 * The base RS block we can feed to the interleaver to find out all