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/libcamera/pipeline/vimc/vimc.cpp

@@ -209,7 +209,7 @@ CameraConfiguration *PipelineHandlerVimc::generateConfiguration(Camera *camera,
 			if (pixelformat.first != formats::BGR888) {
 				LOG(VIMC, Info)
 					<< "Skipping unsupported pixel format "
-					<< pixelformat.first.toString();
+					<< pixelformat.first;
 				continue;
 			}
 		}