s390: Fix an assert.


git-svn-id: svn://svn.valgrind.org/vex/trunk@2610 8f6e269a-dfd6-0310-a8e1-e2731360e62c
diff --git a/priv/host_s390_defs.c b/priv/host_s390_defs.c
index 77ce402..dcfef61 100644
--- a/priv/host_s390_defs.c
+++ b/priv/host_s390_defs.c
@@ -5296,7 +5296,7 @@
 {
    s390_insn *insn = LibVEX_Alloc(sizeof(s390_insn));
 
-   vassert(size == 8);
+   vassert(size == 4 || size == 8);
 
    insn->tag  = S390_INSN_DFP_CONVERT;
    insn->size = size;