dm-verity-fec: fix corrected block count stat

dm-verity-fec: fix corrected block count stat

dm_verity_fec::corrected seems to have been intended to count the number
of corrected blocks.  However, it actually counted the number of calls
to fec_decode_bufs() that corrected at least one error.  That's not the
same thing.  For example, in low-memory situations correcting a single
block can require many calls to fec_decode_bufs().

Fix it to count corrected blocks instead.

Fixes: ae97648e14f7 ("dm verity fec: Expose corrected block count via status")
Cc: Shubhankar Mishra <shubhankarm@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>