Fix an include order

Change-Id: If27d9c12f737c20995df67ac56dc997f1eeee163

aom_dsp/ssim.c

@@ -9,10 +9,10 @@
  * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
  */
 
-#include "aom_dsp/ssim.h"
 #include <assert.h>
 #include <math.h>
 #include "./aom_dsp_rtcd.h"
+#include "aom_dsp/ssim.h"
 #include "aom_ports/mem.h"
 #include "aom_ports/system_state.h"