base-files: change logging for upgrade on fwtool

Remove vn call in favour of v call. This commit serves as preparation
for removing the v function call.

Signed-off-by: Florian Eckert <fe@dev.tdt.de>
[alter slightly to prevent double space after colon]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

package/base-files/files/lib/upgrade/fwtool.sh

@@ -81,12 +81,12 @@ fwtool_check_image() {
 	done
 
 	v "Device $device not supported by this image"
-	vn "Supported devices:"
+	local devices="Supported devices:"
 	for k in $dev_keys; do
 		json_get_var dev "$k"
-		_vn " $dev"
+		devices="$devices $dev"
 	done
-	_v
+	v "$devices"
 
 	return 1
 }