[media] it913x: init tuner on attach

That register is needed to program very first in order to operate
correctly.

[crope@iki.fi: returned sequence back, removed sleep, moved reg
write earlier to prevent populating tuner ops in case of failure]

Cc: <stable@vger.kernel.org> # v3.15+
Signed-off-by: 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>