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>

src/libcamera/ipc_pipe_unixsocket.cpp

@@ -82,10 +82,10 @@ int IPCPipeUnixSocket::sendAsync(const IPCMessage &data)
 	return 0;
 }
 
-void IPCPipeUnixSocket::readyRead(IPCUnixSocket *socket)
+void IPCPipeUnixSocket::readyRead([[maybe_unused]] IPCUnixSocket *socket)
 {
 	IPCUnixSocket::Payload payload;
-	int ret = socket->receive(&payload);
+	int ret = socket_->receive(&payload);
 	if (ret) {
 		LOG(IPCPipe, Error) << "Receive message failed" << ret;
 		return;