libcamera: v4l2_device: Fix operator= definition

While the C++ allows the redefinition of operator= to return an
arbitrary type, it is customary to return a reference to the assigned
value type.

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

src/libcamera/include/v4l2_device.h

@@ -62,7 +62,7 @@ public:
 	V4L2Device(const V4L2Device &) = delete;
 	~V4L2Device();
 
-	void operator=(const V4L2Device &) = delete;
+	V4L2Device &operator=(const V4L2Device &) = delete;
 
 	int open();
 	bool isOpen() const;