intel_sst: fix unload bugs

The current driver remove was erroneous and causes
errors when unloading or loading second time

This patch fixes both of these issues

Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Ramesh Babu K V <ramesh.babu@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>