ext4: iterate over buffer heads correctly in move_extent_per_page()

ext4: iterate over buffer heads correctly in move_extent_per_page()

Orabug: 23331057

[ Upstream commit 87f9a031af48defee9f34c6aaf06d6f1988c244d ]

In commit bcff24887d00 ("ext4: don't read blocks from disk after extents
being swapped") bh is not updated correctly in the for loop and wrong
data has been written to disk. generic/324 catches this on sub-page
block size ext4.

Fixes: bcff24887d00 ("ext4: don't read blocks from disk after extentsbeing swapped")
Signed-off-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
(cherry picked from commit 31a37d7c7ef7b4f90b600fcddd1c385a39f9d34c)

Signed-off-by: Dan Duval <dan.duval@oracle.com>