staging/lustre/llite: Update ll_dir_ioctl pointer casts with __user

When casting unsingned long userspace pointer from ioctl argument to
a pointer suitable for use with userspace access functions, need
to remember to add __user attribute, to make sparse happy.

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>