staging/lustre: fix build when CONFIG_UIDGID_STRICT_TYPE_CHECKS is on

kuid_t/kgid_t are wrappered when CONFIG_UIDGID_STRICT_TYPE_CHECKS is on.
Lustre build is broken because we always treat them as plain __u32.
The patch fixes it. Internally, Lustre always use __u32 uid/gid, and
convert to kuid_t/kgid_t when necessary.

Signed-off-by: Peng Tao <tao.peng@emc.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>