Staging: sep: Use filp->private_data to create proper device instances

Move from using a sep_dev global. The workqueue still uses it and we use the
pointer in order to know if a device was found.

This requires some restructuring as the pci probe and the init module logic
are all rather messed up and only worked by luck.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>