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/pid/fancontroller.cpp b/pid/fancontroller.cpp
index 9b54714..5598c4f 100644
--- a/pid/fancontroller.cpp
+++ b/pid/fancontroller.cpp
@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+#include "config.h"
 
 #include "fancontroller.hpp"