media: i2c: tda1997x: constify snd_soc_component_driver struct

`tda1997x_codec_driver` is not modified after its declaration, and it
is only passed to `devm_snd_soc_register_component()`, which expects
a constant `snd_soc_component_driver`.

Move `tda1997x_codec_driver` to a read-only section by declaring it
const.

Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>