V4L/DVB (5318): Fix tda8290 code for tda827x module

During tuner attach, the pointers to host dev structure
are not set yet, so the I2c adapter needs to be accessed differently.
This patch also does some minor cleanup in the saa7134-dvb module.

Signed-off-by: Hartmut Hackmann <hartmut.hackmann@t-online.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>