libcamera: Replace toString with operator<<() for format classes

Now that format classes implement the stream formatting operator<<(),
use it instead of the toString() function.

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

src/cam/kms_sink.cpp

@@ -194,7 +194,7 @@ int KMSSink::configurePipeline(const libcamera::PixelFormat &format)
 	if (ret) {
 		std::cerr
 			<< "Unable to find display pipeline for format "
-			<< format.toString() << std::endl;
+			<< format << std::endl;
 
 		return ret;
 	}