gstav: Use libavcodec util function for version check

The version of libavutil is printed in the log instead of libavcodec
because avutil_version() returns LIBAVUTIL_VERSION_INT. This can be confusing,
so we should be replace it with avcodec_version().
11 jobs for fix-avcodec-version in 34 minutes and 43 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Preparation
passed #268285
gst indent

00:00:16

passed #268284
manifest

00:00:37

 
  Build
passed #268286
build fedora x86_64

00:04:28

passed #268287
build nodebug fedora x86_64

00:03:56

 
  Test
passed #268288
check fedora

00:03:09

passed #268289
integration testsuites fedora

00:11:20

 
  Full Builds
passed #268291
build cerbero android universal

00:10:57

passed #268292
build cerbero cross win32

00:03:43

passed #268293
build cerbero cross win64

00:04:34

passed #268290
build cerbero fedora x86_64

00:05:53

 
  Apps
passed #268294
android universal examples

00:07:18