libceph: init osd->o_node in create_osd()

libceph: init osd->o_node in create_osd()

The red-black node node in the ceph osd structure is not initialized
in create_osd().  Because this node can be the subject of a
RB_EMPTY_NODE() call later on, we should ensure the node is
initialized properly for that.  Add a call to RB_CLEAR_NODE()
initialize it.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>
(cherry picked from commit f407731d12214e7686819018f3a1e9d7b6f83a02)
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>