V4L/DVB (6890): tda18271: fix typo in RF tracking filter calibration

We want to set bits 1 & 2 on easy programming byte 4, not extended byte 4.

Thanks to David Wong for pointing this out.

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Cc: David Wong <davidtlwong@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>