intel_th: msu: Release resources on removal

Do release the resources when msu subdevice gets removed: stop the
capture if it is active (which is still possible even though the
module in pinned) and free the capture buffers.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reviewed-by: Laurent Fert <laurent.fert@intel.com>