[media] dvb_frontend: fix compile warning

Andreas Oberritter <obi@linuxtv.org> has looked at this and agreed that it is
safe to remove the 'timeout' variable.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>