fix typo in avx2 gcc blend.

source/row_gcc.cc

 // VERSION 2
 /*
  *  Copyright 2011 The LibYuv Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS. All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
@@ skipping 3531 matching lines @@
   "1:                                          \n"
     "vmovdqu    (%2),%%ymm0                    \n"
     "vpunpckhbw %%ymm0,%%ymm0,%%ymm3           \n"
     "vpunpcklbw %%ymm0,%%ymm0,%%ymm0           \n"
     "vpxor      %%ymm5,%%ymm3,%%ymm3           \n"
     "vpxor      %%ymm5,%%ymm0,%%ymm0           \n"
     "vmovdqu    (%0,%2,1),%%ymm1               \n"
     "vmovdqu    (%1,%2,1),%%ymm2               \n"
     "vpunpckhbw %%ymm2,%%ymm1,%%ymm4           \n"
     "vpunpcklbw %%ymm2,%%ymm1,%%ymm1           \n"
-    "vpsubb     %%ymm6,%%ymm1,%%ymm4           \n"
+    "vpsubb     %%ymm6,%%ymm4,%%ymm4           \n"
     "vpsubb     %%ymm6,%%ymm1,%%ymm1           \n"
     "vpmaddubsw %%ymm4,%%ymm3,%%ymm3           \n"
     "vpmaddubsw %%ymm1,%%ymm0,%%ymm0           \n"
     "vpaddw     %%ymm7,%%ymm3,%%ymm3           \n"
     "vpaddw     %%ymm7,%%ymm0,%%ymm0           \n"
     "vpsrlw     $0x8,%%ymm3,%%ymm3             \n"
     "vpsrlw     $0x8,%%ymm0,%%ymm0             \n"
     "vpackuswb  %%ymm3,%%ymm0,%%ymm0           \n"
     "vmovdqu    %%ymm0,(%3,%2,1)               \n"
     "lea        0x20(%2),%2                    \n"
@@ skipping 2034 matching lines @@
   );
 }
 #endif  // HAS_ARGBLUMACOLORTABLEROW_SSSE3
 
 #endif  // defined(__x86_64__) || defined(__i386__)
 
 #ifdef __cplusplus
 }  // extern "C"
 }  // namespace libyuv
 #endif