ASoC: Intel: Don't hold spinlock when calling cancel_work_sync

sst_byt_stream_free() should not hold spinlock when calling
cancel_work_sync().

Reported-by: Kevin Strasser <kevin.strasser@intel.com>
Signed-off-by: Wenkai Du <wenkai.du@intel.com>
Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>