[media] si2157: Add support for Si2147-A30 tuner

This patch adds support for Si2147-A30 tuner. Fairly trivial, no firmware needed for this tuner. However, command 14 00 02 07 01 00 seems to be mandatory. On Si2157 and Si2158 the value 0x0100 is the default value, so this patch does not impact the existing tuners/devices. On Si2147 the default is 0x0000 and I can't get a lock with that value.

While here, fix the return length of the previous set command to 4 bytes.

Signed-off-by: Olli Salonen <olli.salonen@iki.fi>
Acked-by: Antti Palosaari <crope@iki.fi>
Reviewed-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>