SUNRPC: Fix null rpc_clnt dereference in rpc_task_queued tracepoint

Backchannel tasks will not have a reference to the rpc_clnt.  Return -1 for
cl_clid in that case.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Trond Myklebust <trondmy@gmail.com>

include/trace/events/sunrpc.h

@@ -175,7 +175,7 @@ DECLARE_EVENT_CLASS(rpc_task_queued,
 		),
 
 	TP_fast_assign(
-		__entry->client_id = clnt->cl_clid;
+		__entry->client_id = clnt ? clnt->cl_clid : -1;
 		__entry->task_id = task->tk_pid;
 		__entry->timeout = task->tk_timeout;
 		__entry->runstate = task->tk_runstate;
@@ -184,7 +184,7 @@ DECLARE_EVENT_CLASS(rpc_task_queued,
 		__assign_str(q_name, rpc_qname(q));
 		),
 
-	TP_printk("task:%u@%u flags=%4.4x state=%4.4lx status=%d timeout=%lu queue=%s",
+	TP_printk("task:%u@%d flags=%4.4x state=%4.4lx status=%d timeout=%lu queue=%s",
 		__entry->task_id, __entry->client_id,
 		__entry->flags,
 		__entry->runstate,