[media] mantis: trivial module parameter documentation fix

The default for "verbose" is 0.  Update description to match.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Acked-by: Manu Abraham <manu@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>