V4L/DVB (10507): saa7134: Fix analog mode on devices that need to open an i2c gate

Some saa7134 devices require to open an i2c gate before tuning. This
patch fix the initialization for those devices.

The nxt200x_gate_ctrl() logic were returned back to the old place, since
we don't know how to close the gate. A future pacth could revert that
change and provide the proper close gate control, to avoid keeping it
open forever.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>