tcg/s390: Only one call output register needed for 64 bit hosts

The second register is only needed for 32 bit hosts.

Cc: Alexander Graf <agraf@suse.de>
Acked-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

tcg/s390/tcg-target.c

@@ -252,7 +252,9 @@ static const int tcg_target_call_iarg_regs[] = {
 
 static const int tcg_target_call_oarg_regs[] = {
     TCG_REG_R2,
-    TCG_REG_R3,
+#if TCG_TARGET_REG_BITS == 32
+    TCG_REG_R3
+#endif
 };
 
 #define S390_CC_EQ      8