IT9135 RF tuner clock is coming from demodulator. We need enable it
early in demod init, before any tuner I/O. Currently it is enabled
by tuner driver itself, but it is too late and performance will be
reduced as some registers are not updated correctly. Clock is
disabled automatically when demod is put onto sleep.

Cc: <stable@vger.kernel.org> # v3.15+
Cc: Bimow Chen <Bimow.Chen@ite.com.tw>
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>