ipq806x: EA8500 fix sysupgrade over stock firmware

When running sysupgrade for the first time over the second partition
(that still had stock firmware) the rootfs wasn't flashed as there
wasn't enough space.
This happend because stock also uses UBI, but the volume name wasn't
recognised and wasn't deleted before flashing.

Signed-off-by: Adrian Panella <ianchi74@outlook.com>

target/linux/ipq806x/base-files/lib/upgrade/linksys.sh

@@ -55,11 +55,36 @@ platform_do_upgrade_linksys() {
 			CI_UBIPART="rootfs2"
 		fi
 
+
+		# remove "squashfs" vol (in case we are flashing over a stock image, which is also UBI)
+
+		local mtdnum="$( find_mtd_index "$CI_UBIPART" )"
+		if [ ! "$mtdnum" ]; then
+			echo "cannot find ubi mtd partition $CI_UBIPART"
+			return 1
+		fi
+
+		local ubidev="$( nand_find_ubi "$CI_UBIPART" )"
+		if [ ! "$ubidev" ]; then
+			ubiattach -m "$mtdnum"
+			sync
+			ubidev="$( nand_find_ubi "$CI_UBIPART" )"
+		fi
+
+		if [ "$ubidev" ]; then
+
+			local squash_ubivol="$( nand_find_volume $ubidev squashfs )"
+
+			# kill volume
+			[ "$squash_ubivol" ] && ubirmvol /dev/$ubidev -N squashfs || true
+		fi
+
+
+		# complete std upgrade
 		nand_upgrade_tar "$1"
 	}
 	[ "$magic_long" = "27051956" ] && {
 		# check firmwares' rootfs types
-		local target_mtd=$(find_mtd_part $part_label)
 		local oldroot="$(linksys_get_root_magic $target_mtd)"
 		local newroot="$(linksys_get_root_magic "$1")"
 
@@ -80,9 +105,6 @@ linksys_preupgrade() {
 	export RAMFS_COPY_BIN="${RAMFS_COPY_BIN} /bin/mkdir /bin/touch"
 	export RAMFS_COPY_DATA="${RAMFS_COPY_DATA} /etc/fw_env.config /var/lock/fw_printenv.lock"
 
-	[ -f /tmp/sysupgrade.tgz ] && {
-		cp /tmp/sysupgrade.tgz /tmp/syscfg/sysupgrade.tgz
-	}
 }
 
 append sysupgrade_pre_upgrade linksys_preupgrade