rtmpproto: Fix a typo in a comment

Signed-off-by: Martin Storsjö <martin@martin.st>
Merge commit '491805636cef50d3f582bd345e1460eeb739ea48'

* commit '491805636cef50d3f582bd345e1460eeb739ea48':
  rtmpproto: Fix a typo in a comment

Merged-by: Michael Niedermayer <michaelni@gmx.at>