libcamera: pipeline: virtual: Simplify error return

Just return an `std::unique_ptr` constructed from an empty
initializer instead of doing a `reset()` on the existing
`config` variable and returning that. This is simpler.

Signed-off-by: Barnabás Pőcze <pobrn@protonmail.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>

src/libcamera/pipeline/virtual/virtual.cpp

@@ -232,8 +232,7 @@ PipelineHandlerVirtual::generateConfiguration(Camera *camera,
 		default:
 			LOG(Virtual, Error)
 				<< "Requested stream role not supported: " << role;
-			config.reset();
+			return {};
-			return config;
 		}
 
 		std::map<PixelFormat, std::vector<SizeRange>> streamFormats;