rbd: do not duplicate ceph_client pointer in rbd_device
The rbd_device structure maintains a duplicate copy of the
ceph_client pointer maintained in its rbd_client structure. There
appears to be no good reason for this, and its presence presents a
risk of them getting out of synch or otherwise misused. So kill it
off, and use the rbd_client copy only.
Signed-off-by: Alex Elder <elder@dreamhost.com> Signed-off-by: Sage Weil <sage@newdream.net>