JFFS2: Only list each directory entry once

JFFS2: Only list each directory entry once

If multiple versions of a file exist, only the most recent version
should be used. The scheme to write 0 for the inode in older versions
did not work, since this would have required writing to flash.

The only time this caused an issue was listing a directory, where older
versions of the file would still be seen. Since the directory entries
are sorted, just look at the next entry in the list, and if it's the same
move to that entry instead.

Signed-off-by: Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>