meson: OpenMP is supposed to be optional
The code around it checks that it is found, so clearly it was meant to be optional, not arequired. Fixes: cd2832ee ("meson: add an optional OpenMP dependency for AMD tests") Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com> Tested-by: Bernd Kuhls <bernd.kuhls@t-online.de> Reviewed-by: Marek Olšák <marek.olsak@amd.com> Reviewed-by: Eric Engestrom <eric@engestrom.ch> Part-of: <!10286>