Update openbios-ppc to revision 373

Fix boot on CD-ROM.
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6264 c046a42c-6fe2-441c-8c8c-71466251a162

pc-bios/README

@@ -42,7 +42,7 @@
   firmware implementation. The goal is to implement a 100% IEEE
   1275-1994 (referred to as Open Firmware) compliant firmware.
   The included Sparc32 and Sparc64 images are built from SVN revision 237.
-  The included PowerPC image is built from SVN revision 372.
+  The included PowerPC image is built from SVN revision 373.
 
 - The PXE roms come from Rom-o-Matic etherboot 5.4.2.
   pcnet32:pcnet32 -- [0x1022,0x2000]