Write proper start label for loop parameter

compiler/testData/codegen/bytecodeText/forLoop/loopVarInterval.kt

@@ -0,0 +1,9 @@
+fun f() {
+    for (c in "123") {
+        print(c)
+    }
+}
+
+// 1 ISTORE 0\s+L3
+// 1 ILOAD 0\s+INVOKEVIRTUAL java/io/PrintStream.print \(C\)V
+// 1 LOCALVARIABLE c C L3 L8 0