ASoC: Amstrad Delta: fix const related build error

The Amstrad Delta ASoC driver used to override the digital_mute()
callback, expected to be not provided by the on-board CX20442 CODEC
driver, with its own implementation. While this is still posssible when
substituting the whole empty snd_soc_dai_driver.ops member (the CX20442
case), replacing snd_soc_dai_ops.digital_mute only is no longer correct
after the snd_soc_dai_driver.ops member has been constified, and results
in build error.

Drop this actually not used code path in hope the CX20442 driver never
provides its own snd_soc_dai_ops structure.

Created and tested against linux-2.6.38-rc2
Signed-off-by: NJanusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Acked-by: NLiam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/omap/ams-delta.c

@@ -507,8 +507,6 @@ static int ams_delta_cx20442_init(struct snd_soc_pcm_runtime *rtd)
 	/* Set up digital mute if not provided by the codec */
 	if (!codec_dai->driver->ops) {
 		codec_dai->driver->ops = &ams_delta_dai_ops;
-	} else if (!codec_dai->driver->ops->digital_mute) {
-		codec_dai->driver->ops->digital_mute = ams_delta_digital_mute;
 	} else {
 		ams_delta_ops.startup = ams_delta_startup;
 		ams_delta_ops.shutdown = ams_delta_shutdown;