octeon: sysupgrade: fix test for rootfs device

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43522 3c298f89-4303-0410-b956-a3cf2f4a3e73

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

@@ -36,7 +36,7 @@ platform_do_upgrade() {
 	local board=$(octeon_board_name)
 	local rootfs="$(platform_get_rootfs)"
 
-	[ -d "${rootfs}" ] || return 1
+	[ -b "${rootfs}" ] || return 1
 
 	case "$board" in
 	erlite)