hlssink2: Fix string leak

Need to free allocated string memory on _finalize()
3 jobs for fix-leak in 5 minutes and 14 seconds (queued for 1 second)
Status Job ID Name Coverage
  Preparation
passed #51046
manifest

00:00:19

 
  Build
passed #51047
build fedora x86_64

00:02:01

 
  Full Builds
passed #51048
build android arm64 api28

00:02:52