dm verity fec: fix bufio leaks

dm verity fec: fix bufio leaks

BugLink: http://bugs.launchpad.net/bugs/1682130
commit 86e3e83b443669dd2bcc5c8a83b23e3aa0694c0d upstream.

Buffers read through dm_bufio_read() were not released in all code paths.

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