Fix embarrassing typo in fp-vrp.

ir/opt/fp-vrp.c

@@ -324,7 +324,7 @@ undefined:
 					if ((get_Confirm_relation(irn) & ~ir_relation_unordered) == ir_relation_equal) {
 						bitinfo* const bound_b = get_bitinfo(get_Confirm_bound(irn));
 						z = tarval_and(z, bound_b->z);
-						z = tarval_or( o, bound_b->o);
+						o = tarval_or( o, bound_b->o);
 					}
 					break;
 				}