x86/h264_weight: use appropriate register size for weight parameters

This fixes decoding corruption on 64 bit windows.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/x86/h264_weight.asm

@@ -134,16 +134,16 @@ WEIGHT_FUNC_HALF_MM 8, 8
     mov  off_regd, r7m
     add  off_regd, 1
     or   off_regd, 1
-    add        r4, 1
-    cmp        r6d, 128
+    add       r4d, 1
+    cmp       r6d, 128
     je .nonnormal
-    cmp        r5, 128
+    cmp       r5d, 128
     jne .normal
 .nonnormal
-    sar        r5, 1
-    sar        r6, 1
+    sar       r5d, 1
+    sar       r6d, 1
     sar  off_regd, 1
-    sub        r4, 1
+    sub       r4d, 1
 .normal
 %if cpuflag(ssse3)
     movd       m4, r5d