[media] fc0012: enable clock output on attach()

We need feed clock to slave demodulator at the very beginning
in case of dual tuner configuration.
I am not sure if that configuration changes clock output divider
or enable clock output itself...

Signed-off-by: Antti Palosaari <crope@iki.fi>
Acked-by: Hans-Frieder Vogt <hfvogt@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>