[calls] meson: Don't use deprecated meson.source_root()

[Evangelos Ribeiro Tzaras <devrtz src gnome org>]

commit 8f85c42ba38291ca1fdb5330a4293ef1a63dd265
Author: Evangelos Ribeiro Tzaras <devrtz fortysixandtwo eu>
Date:   Wed Dec 29 11:08:54 2021 +0100

    meson: Don't use deprecated meson.source_root()
    
    This function is deprecated since 0.56.0:
    
    WARNING: Project targeting '>= 0.56.0' but tried to use feature deprecated since
    '0.56.0': meson.source_root. use meson.project_source_root() or
    meson.global_source_root() instead.

 doc/meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/doc/meson.build b/doc/meson.build
index 85bddaf6..2daf99cc 100644
--- a/doc/meson.build
+++ b/doc/meson.build
@@ -25,7 +25,7 @@ endif
 gnome.gtkdoc('calls',
            main_xml: 'calls-docs.xml',
             src_dir: [
-                       join_paths(meson.source_root(), 'src'),
+                       join_paths(meson.project_source_root(), 'src'),
                        join_paths(meson.project_build_root(), 'src'),
                        join_paths(meson.project_build_root(), 'src/dbus'),
                        join_paths(meson.project_build_root(), 'plugins/ofono/libgdbofono'),