ASoC: spdif: extend supported rates to 768kHz

IEC958-3 defines sampling rate up to 768 kHz.
Such rates maybe used with high bandwidth IEC958 links, such as eARC.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Acked-by: Mark Brown <broonie@kernel.org>
Reviewed-by: David Rhodes <drhodes@opensource.cirrus.com>
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20240905-alsa-12-24-128-v1-13-8371948d3921@baylibre.com