[media] r820t: proper initialize the PLL register

The rtl-sdr library, from where this driver was initially
based, doesn't use half PLL clock, but this is used on
the Realtek Kernel driver. So, also do the same here.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Tested-by: Antti Palosaari <crope@iki.fi>