libceph: don't use rb_init_node() in ceph_osdc_alloc_request()

The red-black node in the ceph osd request structure is initialized
in ceph_osdc_alloc_request() using rbd_init_node().  We do need to
initialize this, because in __unregister_request() we call
RB_EMPTY_NODE(), which expects the node it's checking to have
been initialized.  But rb_init_node() is apparently overkill, and
may in fact be on its way out.  So use RB_CLEAR_NODE() instead.

For a little more background, see this commit:
    4c199a93 rbtree: empty nodes have no color"

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>
(cherry picked from commit a978fa20fb657548561dddbfb605fe43654f0825)
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/net/ceph/osd_client.c b/net/ceph/osd_client.c
index 6af3d2a..2c39516 100644
--- a/net/ceph/osd_client.c
+++ b/net/ceph/osd_client.c
@@ -221,6 +221,7 @@
 	kref_init(&req->r_kref);
 	init_completion(&req->r_completion);
 	init_completion(&req->r_safe_completion);
+	RB_CLEAR_NODE(&req->r_node);
 	INIT_LIST_HEAD(&req->r_unsafe_item);
 	INIT_LIST_HEAD(&req->r_linger_item);
 	INIT_LIST_HEAD(&req->r_linger_osd);