fix avx2 box filter bug for yuv down sampling.

offset to second group of pixels was off by 16.
should have been 32, not 16.
requires avx2 hardware and wide image for test.

R=harryjin@google.com
TBR=harryjin@google.com
BUG=libyuv:492,libyuv:501

Review URL: https://codereview.chromium.org/1395603002 .

README.chromium

 Name: libyuv
 URL: http://code.google.com/p/libyuv/
-Version: 1502
+Version: 1503
 License: BSD
 License File: LICENSE
 

include/libyuv/version.h

@@ -11,6 +11,6 @@
 #ifndef INCLUDE_LIBYUV_VERSION_H_  // NOLINT
 #define INCLUDE_LIBYUV_VERSION_H_
 
-#define LIBYUV_VERSION 1502
+#define LIBYUV_VERSION 1503
 
 #endif  // INCLUDE_LIBYUV_VERSION_H_  NOLINT

source/scale_gcc.cc

@@ -619,9 +619,9 @@ void ScaleAddRow_AVX2(const uint8* src_ptr, uint16* dst_ptr, int src_width) {
     "vpunpcklbw %%ymm5,%%ymm3,%%ymm2           \n"
     "vpunpckhbw %%ymm5,%%ymm3,%%ymm3           \n"
     "vpaddusw   " MEMACCESS(1) ",%%ymm2,%%ymm0 \n"
-    "vpaddusw   " MEMACCESS2(0x10,1) ",%%ymm3,%%ymm1 \n"
+    "vpaddusw   " MEMACCESS2(0x20,1) ",%%ymm3,%%ymm1 \n"
     "vmovdqu    %%ymm0," MEMACCESS(1) "        \n"
-    "vmovdqu    %%ymm1," MEMACCESS2(0x10,1) "  \n"
+    "vmovdqu    %%ymm1," MEMACCESS2(0x20,1) "  \n"
     "lea       " MEMLEA(0x40,1) ",%1           \n"
     "sub       $0x20,%2                        \n"
     "jg        1b                              \n"