obs-ffmpeg: Fix compilation when ENABLE_HEVC is not set

When ENABLE_HEVC is not set the 'bool hevc' function parameter
is not being used in this function causing a warning and aborting
compilation.
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f