Fix subproject dependency version

[xclaesse]

It must match the pkg-config version which uses va_api_version.

[xclaesse]

For context see https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8793#note_2857006.

[ceyusa]

Let me explain why this change is required:

On one side, libva handles two versions: one for the library and one for the API. The current release, for example, the library is 2.22, while the API is 1.22.

When reporting the library version through pkg-config, libva reports back API version.

It's strange, but it has been as is since ever. No issues.

Nevertheless, meson has the subproject feature as a way to "bundle third party libraries in your source tree". And GStreamer uses it for certain dependencies, as it does for libva.

The problem lies here: by default meson reports back, when a third party library is built as a subproject, the library version (2.22), when in this case we must report back the API version (1.22) in order to keep the same checks when using the library via pkg-config.

And that is what this patch fixes.

So far, this issue has passed unaware because most of the people uses system installed libraries, where the pkg-config is used. Just recently was found out because of H.266 decoder.

[xclaesse]

CC @XinfengZhang