dm-integrity: fix a warning on invalid table line

commit 0a533c3e4246c29d502a7e0fba0e86d80a906b04 upstream.

If we use the 'B' mode and we have an invalit table line,
cancel_delayed_work_sync would trigger a warning. This commit avoids the
warning.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>