drm/i2c: tda998x: use ALSA IEC958 definitions and update audio frequency

This patch sets the frequency as 'not indicated' instead of '48kHz'
and uses the asound values in the channel status definition.

Tested-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>