[media] smsdvb: fix get_frontend

In the get_frontend function, an internal copy of the dtv_frontend_properties
struct (which is never initialized) is copied over the frontend property cache
data structure, resetting everything to 0.
In particular, the delivery system is reset to 0 (which is an invalid value)
so the driver stops working as soon as a DVBv3 application calls the
get_frontend function, giving this error:

dvb_frontend_ioctl_legacy: doesn't know how to handle a DVBv3 call to delivery
system 0

This patch eliminates the unused internal copy of the dtv_frontend_properties
struct, and gives a proper implementation of the get_frontend function.

The original author of the patch is Panagiotis Malakoudis, who also tested
this new version on Ubuntu 11.10 with the latest media_build tree installed.
The original patch has been used on MIPS set-top-boxes for over one year,
but it was never posted on the linux-media list.
I ported the code to the current media_build tree (converting it to use the
dtv_frontend_properties struct) and added basic support for ISDB-T (untested).

Signed-off-by: Panagiotis Malakoudis <malakudi@gmail.com>
Signed-off-by: Gianluca Gennari <gennarone@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>