ASoC: Intel: Skylake: Fix stereo DMIC record

DMIC BE can have 2 or 4 channels supported. The DMIC fixup needs
to take this into account.

Signed-off-by: Jeeja KP <jeeja.kp@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>