xen: adding missing break.

Thanks to Julien Grall.

From: Ian Campbell <ian.campbell@citrix.com>


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13048 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/coregrind/m_syswrap/syswrap-xen.c b/coregrind/m_syswrap/syswrap-xen.c
index 6226f7e..3557ba1 100644
--- a/coregrind/m_syswrap/syswrap-xen.c
+++ b/coregrind/m_syswrap/syswrap-xen.c
@@ -127,6 +127,7 @@
          PRE_MEM_READ(which,
                       (Addr)memory_reservation->extent_start.p,
                       sizeof(xen_pfn_t) * memory_reservation->nr_extents);
+	 break;
       case XENMEM_populate_physmap:
          which = "XENMEM_populate_physmap";
          PRE_MEM_READ(which,