[pcm] Link to sample needs fixing

[tidoust]

The linear PCM registration includes a link to the notion of sample ([=sample=] in the source). I suppose it's meant to target the definition of sample in Webcodecs but WebCodecs does not yet export the term. The cross-references database made Bikeshed link to sample in CSP 3. A new sample has emerged in WGSL, which makes Bikeshed report a warning. In any case, the link needs fixing.

Via #881.