[omx] Fix compile warning after PR 5348.

I actually think that code is not even executed, so this doesn't only fix the warning.

Edit: https://github.com/Phaeodaria/xbmc/commit/77778e4e1ef549455574f765ff6252fbb278effa#diff-41e0ceb3de6f45669f617deae0dbeb0cR2674