ASoC: SOF: Fix potential NULL pointer dereference

Cleanup path for sof_prepare_widgets_in_path() should check if unprepare
callback exists before calling it, instead it checks if it does not
exist. Fix the check.

Signed-off-by: Amadeusz Sławiński <amadeuszx.slawinski@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Link: https://lore.kernel.org/r/20220602135757.3335351-1-amadeuszx.slawinski@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>