target-s390: Use uint64_to_float128

Signed-off-by: Richard Henderson <rth@twiddle.net>

target-s390x/fpu_helper.c

diff --git a/target-s390x/fpu_helper.c b/target-s390x/fpu_helper.c
index 58c2e61..b6e5040 100644
--- a/target-s390x/fpu_helper.c
+++ b/target-s390x/fpu_helper.c
@@ -419,8 +419,7 @@
 uint64_t HELPER(cxlgb)(CPUS390XState *env, uint64_t v2, uint32_t m3)
 {
     int hold = swap_round_mode(env, m3);
-    /* ??? Not 50% correct.  */
-    float128 ret = int64_to_float128(v2, &env->fpu_status);
+    float128 ret = uint64_to_float128(v2, &env->fpu_status);
     set_float_rounding_mode(hold, &env->fpu_status);
     handle_exceptions(env, GETPC());
     return RET128(ret);