opkg-nogpg: add file path

opkg-nogpg: add file path

There was no explicit path in FILESPATH for this recipe to allow it to
find files referred to in SRC_URI (files shared with the standard opkg
recipe). This problem may have been masked by the fetcher behaviour of
looking for files last in DL_DIR, thus if opkg has been fetched
beforehand there would have been no error.

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>