docs: Fix a misdirected kerneldoc directive

The stratix10 service layer documentation tried to include a kerneldoc
comments for a nonexistent struct; leading to a "no structured comments
found" message.  Switch it to stratix10_svc_command_config_type, which
appears at that spot in the sequence and was not included.

Signed-off-by: Jonathan Corbet <corbet@lwn.net>