V4L/DVB (13360): stv090x: fix the calculation of the r divider in stv6110x_set_frequency

It had always the value 3 no matter what frequency was given.

Signed-off-by: Andreas Regel <andreas.regel@gmx.de>
Signed-off-by: Manu Abraham <manu@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>