V4L/DVB (6723): tda18271: only force init once during attach

Once the image rejection calibration procedure has been successful,
we should not initialize the tuner registers again.

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>