ASoC: soc-pcm: Remove unused 'debugfs_dpcm_state' entry

'debugfs_dpcm_state' member from structure snd_soc_pcm_runtime
is never used at all, so it is safe to remove it.

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