Sparc32: Update OpenBIOS image to r666

Fixes the boot problem introduced by r665 image in
694b9309.
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

pc-bios/README

@@ -15,7 +15,7 @@
   firmware implementation. The goal is to implement a 100% IEEE
   1275-1994 (referred to as Open Firmware) compliant firmware.
   The included images for PowerPC (for 32 and 64 bit PPC CPUs) are built from
-  OpenBIOS SVN revision 640, Sparc32 and Sparc64 images from r665.
+  OpenBIOS SVN revision 640, Sparc64 images from r665 and Sparc32 from r666.
 
 - The PXE roms come from Rom-o-Matic gPXE 0.9.9 with BANNER_TIMEOUT=0