[grilo] Fix build with recent Meson

[Emmanuele Bassi <ebassi src gnome org>]

commit 3104a340a674429a01a41fbce8441728660077e4
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Sat Mar 11 23:07:06 2017 +0000

    Fix build with recent Meson
    
    Referencing the current source directory inside an include_directories()
    statement is not recommended in Meson, and version 0.39, released on
    March 5th, declares it an error.

 src/meson.build |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/meson.build b/src/meson.build
index 08a742a..36c34b3 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -79,8 +79,8 @@ install_headers(grl_headers,
     subdir: grl_name)
 
 libgrl_inc = include_directories([
-    meson.current_source_dir(),
-    '@0@/data'.format(meson.current_source_dir()),
+    '.',
+    'data',
 ])
 
 c_args = [