fix missing access service items when parsing dataset

[SebastianEsp]

When parsing datasets with a dcat:DataService the "endpoint_url" and "serves_dataset" properties are never added to the resource_dict due to a mislabeled variable name

Fx. a dataset with the following DataService:

<dcat:DataService rdf:about="https://example.com/dataservice1">
  <dcterms:title xml:lang="sv">API exempel</dcterms:title>
  <dcat:keyword xml:lang="sv">bibliotek</dcat:keyword>
  <dcat:keyword xml:lang="en">library</dcat:keyword>
  <dcat:contactPoint rdf:resource="https://example.com/contactpoint1"/>
  <dcterms:license rdf:resource="http://creativecommons.org/publicdomain/zero/1.0/"/>
  <dcterms:accessRights rdf:resource="http://publications.europa.eu/resource/authority/access-right/PUBLIC"/>
  <dcat:endpointURL rdf:resource="http://example.com/api"/>
  <dcat:endpointDescription rdf:resource="http://example.com/apidescription"/>
  <dcat:servesDataset rdf:resource="https://example.com/dataset1" />
</dcat:DataService>

will return the following output when requesting the .rdf representation of the dataset:

<dcat:DataService rdf:about="https://example.com/dataservice1">
  <dct:license rdf:resource="http://creativecommons.org/publicdomain/zero/1.0/"/>
  <dct:accessRights rdf:resource="http://publications.europa.eu/resource/authority/access-right/PUBLIC"/>
  <dct:title>API exempel</dct:title>
  <dcat:endpointDescription>http://example.com/apidescription</dcat:endpointDescription>
</dcat:DataService>

[seitenbau-govdata]

Thanks for the fix @SebastianEsp