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/ipa/ipa_interface_test.cpp

@@ -153,9 +153,9 @@ protected:
 	}
 
 private:
-	void readTrace(EventNotifier *notifier)
+	void readTrace([[maybe_unused]] EventNotifier *notifier)
 	{
-		ssize_t s = read(notifier->fd(), &trace_, sizeof(trace_));
+		ssize_t s = read(notifier_->fd(), &trace_, sizeof(trace_));
 		if (s < 0) {
 			int ret = errno;
 			cerr << "Failed to read from IPA test FIFO at '"