[IA64] update the comment in ia64_switch_to.

update the comment in ia64_switch_to.

Signed-off-by: Isaku Yamahata <yamahata@xxxxxxxxxxxxx>

diff -r 11409f11697c xen/arch/ia64/linux-xen/entry.S
--- a/xen/arch/ia64/linux-xen/entry.S	Thu Aug 07 18:26:52 2008 +0900
+++ b/xen/arch/ia64/linux-xen/entry.S	Thu Aug 07 18:27:44 2008 +0900
@@ -265,7 +265,7 @@
 	srlz.d
 	or r23=r25,r20			// construct PA | page properties
 #ifdef XEN
-	ptr.d in0,r27			// to purge dtr[IA64_TR_VHPT]
+	ptr.d in0,r27			// to purge dtr[IA64_TR_VHPT] and dtr[IA64_TR_VPD]
 #else
 	movl r27=IA64_GRANULE_SHIFT << 2	
 #endif