libcamera: Don't use emitter object pointer argument to slot

In many cases, the emitter object passed as a pointer from signals to
slots is also available as a class member. Use the class member when
this occurs, to prepare for removal of the emitter object pointer from
signals.

In test/event.cpp, this additionally requires moving the EventNotifier
to a class member.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>

test/event-thread.cpp

@@ -66,9 +66,9 @@ public:
 	}
 
 private:
-	void readReady(EventNotifier *notifier)
+	void readReady([[maybe_unused]] EventNotifier *notifier)
 	{
-		size_ = read(notifier->fd(), data_, sizeof(data_));
+		size_ = read(notifier_->fd(), data_, sizeof(data_));
 		notified_ = true;
 	}