[IA64] r23 was used without being set

There is one small problem.  In mca_asm.S, r23 was used without being set 
and the hardcoded value 40 is no longer valid (patch below).

With linux-ia64-test-2.6.11 plus David's patch plus the patch
below, 1024 memory uncorectable errors were injected and sucessfully
recovered on an SGI Altix test machine.  1024 is the number of entries 
in the page_isolate[] array in arch/ia64/kernel/mca_drv.c.  When the 
array is full, the recovery code says the error is not recoverable 
and the system reboots.
Signed-off-by: Russ Anderson <rja@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/kernel/mca_asm.S

@@ -203,9 +203,9 @@ begin_tlb_purge_and_reload:
 	srlz.d
 	;;
 	// 3. Purge ITR for PAL code.
-	adds r17=40,r23
+	GET_THIS_PADDR(r2, ia64_mca_pal_base)
 	;;
-	ld8 r16=[r17]
+	ld8 r16=[r2]
 	mov r18=IA64_GRANULE_SHIFT<<2
 	;;
 	ptr.i r16,r18