ASoC: dapm: Initialize private_value in snd_soc_dapm_new_dai

In case of single config, private_value is left uninitialized.

The private_value does need to be initialized or in
snd_soc_dapm_new_control_unlocked() call failure case, it leads to a
bogus free in snd_soc_dapm_free_kcontrol()

Signed-off-by: Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>