ASoC: topology: Fix to add dapm mixer info

Mixer control for widgets can't be created if the info is NULL. So assign
the correct info for this.

Signed-off-by: Jeeja KP <jeeja.kp@intel.com>
Signed-off-by: Subhransu S. Prusty <subhransu.s.prusty@intel.com>
Acked-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>