ixp4xx: fix Avila SoC audio driver compilation

Upstream dropped the `dapm` member of `struct snd_soc_component`, requiring
users to access it using `snd_soc_codec_get_dapm()` instead so change the
driver code to do just that.

Fixes the following build error spotted by the buildbots:

      CC [M]  sound/soc/gw-avila/gw-avila.o
    sound/soc/gw-avila/gw-avila.c: In function 'avila_aic3x_init':
    sound/soc/gw-avila/gw-avila.c:104:44: error: 'struct snd_soc_codec' has no member named 'dapm'

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

target/linux/ixp4xx/patches-4.4/175-avila_hss_audio_support.patch

@@ -641,7 +641,7 @@
 +static int avila_aic3x_init(struct snd_soc_pcm_runtime *rtd)
 +{
 +	struct snd_soc_codec *codec = rtd->codec;
-+	struct snd_soc_dapm_context *dapm = &codec->dapm;
++	struct snd_soc_dapm_context *dapm = snd_soc_codec_get_dapm(codec);
 +
 +  /* Add davinci-evm specific widgets */
 +  snd_soc_dapm_new_controls(dapm, aic3x_dapm_widgets,