Include VPXMAX definition in mr_dissim.c

This might be getting included in some transitive way
in the upstream builds. Will fix there.

R=tomfinegan@chromium.org

Review URL: https://codereview.chromium.org/1309263003 .
diff --git a/source/libvpx/vp8/encoder/mr_dissim.c b/source/libvpx/vp8/encoder/mr_dissim.c
index 7d05d93..4bf36e8 100644
--- a/source/libvpx/vp8/encoder/mr_dissim.c
+++ b/source/libvpx/vp8/encoder/mr_dissim.c
@@ -16,6 +16,7 @@
 #include "vpx_mem/vpx_mem.h"
 #include "rdopt.h"
 #include "vp8/common/common.h"
+#include "vpx_dsp/vpx_dsp_common.h"
 
 void vp8_cal_low_res_mb_cols(VP8_COMP *cpi)
 {