yaffs direct: Fix opening of a directory.

yaffs direct: Fix opening of a directory.

If opening a directory using yaffs_open(), Yaffs Direct was checking
that the file was being opened with O_RDONLY.

In fact those flags should actually be ignored and it should be treated
as if opened O_RDONLY.

Therefore override flags if opening a directory.

Signed-off-by: Charles Manning <cdhmanning@gmail.com>