fs/adfs: newdir: merge adfs_dir_read() into adfs_f_read()

adfs_dir_read() is only called from adfs_f_read(), so merge it into
that function.  As new directories are always 2048 bytes in size,
(which we rely on elsewhere) we can consolidate some of the code.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>