treewide: replace /sys/devices/virtual/ubi by /sys/class/ubi

Starting from Linux Kernel version 6.3 UBI devices will no longer be
considered virtual, but rather have an MTD device parent. Hence they
will no longer be listed under /sys/devices/virtual/ubi which is
used in multiple places in OpenWrt. Prepare for future kernels by
using /sys/class/ubi instead of /sys/devuces/virtual/ubi.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

target/linux/ipq40xx/base-files/lib/upgrade/linksys.sh

@@ -3,7 +3,7 @@ linksys_get_target_firmware() {
 
 	cur_boot_part="$(/usr/sbin/fw_printenv -n boot_part)"
 	if [ -z "${cur_boot_part}" ]; then
-		mtd_ubi0=$(cat /sys/devices/virtual/ubi/ubi0/mtd_num)
+		mtd_ubi0=$(cat /sys/class/ubi/ubi0/mtd_num)
 		case "$(grep -E "^mtd${mtd_ubi0}:" /proc/mtd | cut -d '"' -f 2)" in
 		kernel|rootfs)
 			cur_boot_part=1