Disambiguate registermap assertion report

registerMap/export/c/elements/field.py line 38

    @property
    def type( self ) :
        assert self._element[ 'size' ] <= max( [ x for x in self.__knownTypes.keys() ] ), \
-->>            'Bad size for field, {0}, {1}'.format(self._element[ 'size' ], self._element.canonicalId)