Fix 'netapp_e_lun_mapping ... documentation error' (#2966)

The 'short_description' in netapp_e_lun_mapping was a
list instead of txt.

This fixes errors on 'ansible-doc -l' of form:

        ERROR! module netapp_e_lun_mapping has a documentation
        error formatting or is missing documentation

Fixes: #17634 (ansible/ansible)

lib/ansible/modules/extras/storage/netapp/netapp_e_lun_mapping.py

@@ -21,8 +21,7 @@ DOCUMENTATION = '''
 ---
 module: netapp_e_lun_mapping
 author: Kevin Hulquest (@hulquest)
-short_description:
+short_description: Create or Remove LUN Mappings
-     - Create or Remove LUN Mappings
 description:
      - Allows for the creation and removal of volume to host mappings for NetApp E-series storage arrays.
 version_added: "2.2"