tuner: Do not alter i2c_client.name

The tuner driver used to change i2c_client.name for its own needs, but
it really shouldn't, as this field is used by i2c-core to do the
device/driver matching. So, create and use a separate field for the
tuner driver needs.

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Jean Delvare <khali@linux-fr.org>