octeon: use shared function for platform_copy_config()

This reduces redundant instructions.

The solution is inspired by a different implemention of
Roman Kuzmitskii.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/octeon/base-files/lib/upgrade/platform.sh

@@ -1,5 +1,5 @@
 #
-# Copyright (C) 2014 OpenWrt.org
+# Copyright (C) 2021 OpenWrt.org
 #
 
 platform_get_rootfs() {
@@ -17,23 +17,25 @@ platform_get_rootfs() {
 	fi
 }
 
+platform_copy_config_helper() {
+	local device=$1
+
+	mount -t vfat "$device" /mnt
+	cp -af "$UPGRADE_BACKUP" "/mnt/$BACKUP_FILE"
+	umount /mnt
+}
+
 platform_copy_config() {
 	case "$(board_name)" in
 	erlite)
-		mount -t vfat /dev/sda1 /mnt
-		cp -af "$UPGRADE_BACKUP" "/mnt/$BACKUP_FILE"
-		umount /mnt
+		platform_copy_config_helper /dev/sda1
 		;;
 	itus,shield-router)
-		mount -t vfat /dev/mmcblk1p1 /mnt
-		cp -af "$UPGRADE_BACKUP" "/mnt/$BACKUP_FILE"
-		umount /mnt
+		platform_copy_config_helper /dev/mmcblk1p1
 		;;
-	ubnt,edgerouter-4 | \
+	ubnt,edgerouter-4|\
 	ubnt,edgerouter-6p)
-		mount -t vfat /dev/mmcblk0p1 /mnt
-		cp -af "$UPGRADE_BACKUP" "/mnt/$BACKUP_FILE"
-		umount /mnt
+		platform_copy_config_helper /dev/mmcblk0p1
 		;;
 	esac
 }