libcamera: stream: Qualify 'Camera' friend directive

Align the Stream class to all other classes in the code base to use the
'class' qualifier in 'friend' declarations.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>

include/libcamera/stream.h

@@ -29,7 +29,7 @@ public:
 	const StreamConfiguration &configuration() const { return configuration_; }
 
 private:
-	friend Camera;
+	friend class Camera;
 
 	BufferPool bufferPool_;
 	StreamConfiguration configuration_;