apps: cam: Do not overwrite name when adding camera model

If `addModel` is true, then the previously set `name` will be overwritten.
This does not seem to be the intended behaviour, so fix it by using `+=`.

Before:

  Available cameras:
  1: 'imx219' (/base/soc@0/bus@30800000/i2c@30a30000/camera@10)

After:

  Available cameras:
  1: External camera 'imx219' (/base/soc@0/bus@30800000/i2c@30a30000/camera@10)

Fixes: aab49f903e ("cam: Do not assume Location is available")
Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/apps/cam/main.cpp

@@ -337,7 +337,7 @@ std::string CamApp::cameraName(const Camera *camera)
 		 */
 		const auto &model = props.get(properties::Model);
 		if (model)
-			name = "'" + *model + "' ";
+			name += "'" + *model + "' ";
 	}
 
 	name += "(" + camera->id() + ")";