ceph: fix request time stamp encoding

struct timespec uses 'long' to present second and nanosecond. 'long'
is 64 bits on 64bits machine. ceph MDS expects time stamp to be
encoded as struct ceph_timespec, which uses 'u32' to present second
and nanosecond.

Signed-off-by: Yan, Zheng <zyan@redhat.com>