ASoC: Intel: Skylake: Fix not to stop src pipe in pre pmd event handler

If the widget is a mixin module, just unbind between source and sink
and don't stop the source pipe as there can be multiple sinks
connected.

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