mediatek: filogic: avoid sub-shell invovation in netdev rename loop

Rename network devices to their label set in DT without invocation of
a sub-shell.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
(cherry picked from commit 983222605c)

target/linux/mediatek/filogic/base-files/lib/preinit/04_set_netdev_label

@@ -5,8 +5,8 @@ set_netdev_labels() {
 
 	for dir in /sys/class/net/*; do
 		[ -r "$dir/of_node/label" ] || continue
-		label="$(cat "$dir/of_node/label")"
-		netdev="$(basename $dir)"
+		read -r label < "$dir/of_node/label"
+		netdev="${dir##*/}"
 		[ "$netdev" = "$label" ] && continue
 		ip link set "$netdev" name "$label"
 	done