staging: lustre: include: linux: libcfs: use __packed instead of __attribute__((packed))

This patch fixes checpatch.pl warning in libcfs_debug.h file.
WARNING: __packed is preferred over __attribute__((packed))

Signed-off-by: Tapasweni Pathak <tapaswenipathak@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>