pseries: Update SLOF firmware image

This patch updates the SLOF submodule and precompiled image.  The new
SLOF versions contains two changes of note:

 * The previous SLOF has a bug in SCSI condition handling that was
   exposed by recent updates to qemu's SCSI emulation.  This update
   fixes the bug.

 * The previous SLOF has a bug in its addressing of SCSI devices,
   which can be exposed under certain conditions.  The new SLOF also
   fixes this.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>

pc-bios/README

@@ -17,7 +17,7 @@
 - SLOF (Slimline Open Firmware) is a free IEEE 1275 Open Firmware
   implementation for certain IBM POWER hardware.  The sources are at
   https://github.com/dgibson/SLOF, and the image currently in qemu is
-  built from git tag qemu-slof-20110323.
+  built from git tag qemu-slof-20110930.
 
 - The PXE roms come from the iPXE project. Built with BANNER_TIME 0.
   Sources available at http://ipxe.org.  Vendor:Device ID -> ROM mapping: