intel_sst: make sure the sst_drop_stream() get called when needed

When "aplay test.wav", if we "ctrl+z" to suspend it, the last piece of
sound will be played endlessly. So we need make sure the drop_stream
is called in such a case.

Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>