media: dvb_frontend: get rid of property cache's state

In the past, I guess the idea was to use state in order to
allow an autofush logic. However, in the current code, it is
used only for debug messages, on a poor man's solution, as
there's already a debug message to indicate when the properties
got flushed.

So, just get rid of it for good.

Reviewed-by: Shuah Khan <shuahkg@osg.samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>