greybus: greybus_trace: Fix broken greybus ftrace

Enabling greybus ftrace event causes null pointer access due to
that gb_message to SVC has no Bundle. Fix it by handling this in
the trace header.

Testing Done:
$ echo 1 > /d/tracing/event/greybus/enable
 [002] ...1    54.504426: gb_message_send: greybus:1-svc op=0023 if_id=0 hd_id=0 l=0
 [002] ...1    54.504461: gb_host_device_send: greybus:greybus1 if_id=0 l=8
Signed-off-by: David Lin <dtwlin@google.com>
Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/greybus_trace.h

@@ -17,6 +17,11 @@
 struct gb_message;
 struct gb_host_device;
 
+#define gb_bundle_name(message)                                  \
+	(message->operation->connection->bundle ?                 \
+	dev_name(&message->operation->connection->bundle->dev) :  \
+	dev_name(&message->operation->connection->hd->svc->dev))
+
 DECLARE_EVENT_CLASS(gb_message,
 
 	TP_PROTO(struct gb_message *message),
@@ -24,7 +29,7 @@ DECLARE_EVENT_CLASS(gb_message,
 	TP_ARGS(message),
 
 	TP_STRUCT__entry(
-		__string(name, dev_name(&message->operation->connection->bundle->dev))
+		__string(name, gb_bundle_name(message))
 		__field(u16, op_id)
 		__field(u16, intf_cport_id)
 		__field(u16, hd_cport_id)
@@ -32,7 +37,7 @@ DECLARE_EVENT_CLASS(gb_message,
 	),
 
 	TP_fast_assign(
-		__assign_str(name, dev_name(&message->operation->connection->bundle->dev))
+		__assign_str(name, gb_bundle_name(message))
 		__entry->op_id = message->operation->id;
 		__entry->intf_cport_id =
 			message->operation->connection->intf_cport_id;