media: cx25840: Use subdev host data for PLL override

The cx25840 driver currently configures 885, 887, and 888 using
default divisors for each chip. This check to see if the cx23885
driver has passed the cx25840 a non-default clock rate for a
specific chip. If a cx23885 board has left clk_freq at 0, the
clock default values will be used to configure the PLLs.

This patch only has effect on 888 boards who set clk_freq to 25M.

Signed-off-by: Brad Love <brad@nextdimension.cc>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>