video-anc: Add comment about our assumption of the ADF user data format

We assume here the same data format for the user data as for the
DID/SDID: 10 bits with parity in the upper 2 bits. In theory some
standards could define this differently and even have full 10 bits of
user data but there does not seem to be a single such standard after
all these years.
2 jobs for vbiparse-fixes in 3 minutes and 54 seconds (queued for 34 seconds)
Status Job ID Name Coverage
  Manifest
passed #42859
manifest

00:01:17

 
  Build
passed #42860
build fedora x86_64

00:02:36