h264_weight: Fix SSSE3 biweight code with weights of 128

CC: libav-stable@libav.org
Sample-Id: test_bref.mp4

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>

libavcodec/x86/h264_weight.asm

@@ -135,6 +135,16 @@ WEIGHT_FUNC_HALF_MM 8, 8
     add  off_regd, 1
     or   off_regd, 1
     add        r4, 1
+    cmp        r6d, 128
+    je .nonnormal
+    cmp        r5, 128
+    jne .normal
+.nonnormal
+    sar        r5, 1
+    sar        r6, 1
+    sar  off_regd, 1
+    sub        r4, 1
+.normal
 %if cpuflag(ssse3)
     movd       m4, r5d
     movd       m0, r6d