fs/adfs: newdir: clean up adfs_f_update()

__adfs_dir_put() and adfs_dir_find_entry() are only called from
adfs_f_update(), so move them into this function, removing some
unnecessary entry copying by doing so.

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