highbd_quantize_intrin_sse2.c: add missing rtcd include

quiets -Wmissing-prototypes warnings

BUG=b/29584271

Change-Id: Iff5214df0d1781810afbfc20bfaf664f109e2f29

vpx_dsp/x86/highbd_quantize_intrin_sse2.c

@@ -10,6 +10,7 @@
 
 #include <emmintrin.h>
 
+#include "./vpx_dsp_rtcd.h"
 #include "vpx_dsp/vpx_dsp_common.h"
 #include "vpx_mem/vpx_mem.h"
 #include "vpx_ports/mem.h"