Fix issues with atf-check(1) found by igor and refer to atf-check(1)

• Fix typo (specifiying -> specifying)
• Add atf-check(1) to SEE ALSO section for completeness. It's mentioned above, but by convention the SEE ALSO section should list all relevant references to other tools and APIs.

Bump .Dd for the change

MFC after: 1 week
Sponsored by: Dell EMC Isilon