meson option requires config.h for meson options to operate properly

This was removed in
https://github.com/openbmc/phosphor-pid-control/commit/f8b6e55

Change-Id: I42d21365516a104cc0372d1fa72477642784c4d1
Signed-off-by: Pete O_o <pmb@meta.com>
diff --git a/dbus/dbushelper.cpp b/dbus/dbushelper.cpp
index 2d50c72..b29d0d6 100644
--- a/dbus/dbushelper.cpp
+++ b/dbus/dbushelper.cpp
@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+#include "config.h"
+
 #include "dbushelper.hpp"
 
 #include "dbushelper_interface.hpp"