meson: switch pkgconfig access method

Since meson (>=0.56) the use of `get_pkgconfig_variable()` is deprecated
in favor of the more arbitrary `get_variable()`. See [reference][]
under: "Arbitrary variables from dependencies that can be found multiple
ways".

[Reference]: https://github.com/mesonbuild/meson/blob/master/docs/markdown/Dependencies.md

Signed-off-by: Patrik Tesarik <patrik.tesarik@9elements.com>
Change-Id: I89d877108f75a4a48f644a75c1fd0e3703e7e1fb
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
1 file changed