fix: debugdvb arg typo

[hrideshmg]

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Came across this issue while trying to debug #985, passing --debugdvbsub to a ccextractor build built with rust would error citing an unknown argument. Turned out to be a simple typo in the rust arg parser.

Here is the entry on ccextractor --help:

--debugdvbsub
          Write the DVB subtitle debug traces to console