bitmap: Avoid shadowing type name with parameter name

[ccan] / test / test.xml1

<xmlthisisaverylongtagnameIhopeitmesseswithyourstuff>
        foobar
        <one foobar barfoo="Hello \"World\"!" foo=bar>
                <two/>
        
        </one>
        <one></one>
        <one></one>
</xml>