qcam: Add JPEG format support

When the camera provides MJPEG, use the QImage JPEG decompression code
to convert that to RGB.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/qcam/main_window.cpp

@@ -222,7 +222,7 @@ int MainWindow::display(Buffer *buffer)
 
 	Plane &plane = buffer->planes().front();
 	unsigned char *raw = static_cast<unsigned char *>(plane.mem());
-	viewfinder_->display(raw);
+	viewfinder_->display(raw, buffer->bytesused());
 
 	return 0;
 }