staging: unisys: Clean up device sysfs attributes

Properly hook into the struct device groups element.  This allows the
core infrastructure to manage the files instead of the bus layer.  And
makes the code easier to read.

I didn't clean up the _show functions just modified them a bit to handle
the different args for now and to prevent a build warning.

Signed-off-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>