dm writecache: fix the maximum number of arguments

commit 67aa3ec3 upstream.

Advance the maximum number of arguments to 16.
This fixes issue where certain operations, combined with table
configured args, exceed 10 arguments.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Fixes: 48debafe ("dm: add writecache target")
Cc: stable@vger.kernel.org # v4.18+
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>