ASoC: soc-generic-dmaengine-pcm: Fix sparse warnings

ASoC: soc-generic-dmaengine-pcm: Fix sparse warnings

Currently the following sparse warnings are observed:

sound/soc/soc-generic-dmaengine-pcm.c:185:34: warning: restricted snd_pcm_format_t degrades to integer
sound/soc/soc-generic-dmaengine-pcm.c:186:66: warning: incorrect type in argument 1 (different base types)
sound/soc/soc-generic-dmaengine-pcm.c:186:66:    expected restricted snd_pcm_format_t [usertype] format
sound/soc/soc-generic-dmaengine-pcm.c:186:66:    got int [signed] [assigned] i

Fix it by changing the loop variable to be of 'snd_pcm_format_t'.

Also introduce a SNDRV_PCM_FORMAT_FIRST label, which corresponds to the
first member (index 0) of the snd_pcm_format_t formats.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>