media: dvb_frontend: get rid of get_property() callback

Only lg2160 implement gets_property, but there's no need for that,
as no other driver calls this callback, as get_frontend() does the
same, and set_frontend() also calls lg2160 get_frontend().

So, get rid of it.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Reviewed-by: Michael Ira Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>