ceph: remove the bump of i_version

Eventually, we'll want to wire cephfs up to use the change attribute
that the cluster tracks instead, but for now this is unneeded.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>