staging: greybus: fix checkpatch unsigned warnings

Fix checkpatch warnings for parameter type unsigned in greybus.
Note that this patch does not fix all checkpatch warnings for the
affected files.

Signed-off-by: Christian Bewermeyer <christian.bewermeyer@fau.de>
Signed-off-by: Roman Sommer <roman.sommer@fau.de>
Reviewed-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>