Fix byte code register dump output

The first register allocated in bindings is typically the return address
register, which was erroneously shown as argument 0 instead of register 0.

Change-Id: I00add0b5b1cd08a4c9b1d42ffe79d2ea7e5a73cf
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/qml/compiler/qv4instr_moth.cpp

@@ -157,7 +157,7 @@ QString dumpRegister(int reg, int nFormals)
     else if (reg == CallData::Argc)
         return QStringLiteral("(argc)");
     reg -= CallData::OffsetCount;
-    if (reg <= nFormals)
+    if (reg < nFormals)
         return QStringLiteral("a%1").arg(reg);
     reg -= nFormals;
     return QStringLiteral("r%1").arg(reg);