nubus: Fix nubus_rewinddir

A long forgotten fix from the linux-mac68k CVS:

Initialize dir->done pointer in nubus_rewinddir().

The original commit is here:

http://linux-mac68k.cvs.sourceforge.net/viewvc/linux-mac68k/linux-mac68k/drivers/nubus/nubus.c?r1=1.22&r2=1.22.2.1&pathrev=linux-2_2



Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>