fs: ceph: Delete timespec64_trunc() usage

Since ceph always uses ns granularity, skip the
truncation which is a no-op.

Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Cc: jlayton@kernel.org
Cc: ceph-devel@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>