staging: kpc2000: introduce usage of __packed

Replaced __attribute__((packed)) with __packed. Both ways of attributing
are equivalent, but being shorter, __packed should be preferred.
This refactoring makes the core more readable.

Signed-off-by: Fabian Krueger <fabian.krueger@fau.de>
Signed-off-by: Michael Scheiderer <michael.scheiderer@fau.de>
Cc: <linux-kernel@i4.cs.fau.de>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>