ASoC: dapm: Remove unused long_name field from snd_soc_dapm_path struct

Since commit 85762e71 ("ASoC: dapm: Implement mixer control sharing") the
long_name field of the snd_soc_dapm_path struct is unused. All of the name
handling now happens entirely in dapm_create_or_share_mixmux_kcontrol(). So we
can remove the long_name field from the snd_soc_dapm_path struct.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>