devmatch: Be tolerant of .ko being present.

We document that we did not need .ko on the module names in
devmatch_blocklist, but we really needed them. Keep the documentation
the same, but strip the .ko when we need to use the names so you can
specify either.

PR: 256240
MFC After: 2 weeks
Sponsored by: Netflix

(cherry picked from commit b29ebb9c65b350e78aedfc790bfcaf9717059b70)