ubox: fix extroot after kmodloader changes

The kmodloader executable disregarded the global directory prefix in
scan_module_folder() leading to a broken extroot for non-builtin modules.

Update to current git head to fix the prefix handling again.

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@38392 3c298f89-4303-0410-b956-a3cf2f4a3e73