Simplify vsad16_mmx().

Originally committed as revision 13191 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/i386/dsputilenc_mmx.c

@@ -760,16 +760,15 @@ static int vsad16_mmx(void *v, uint8_t * pix1, uint8_t * pix2, int line_size, in
       "movq 8(%1),%%mm3\n"
       "add %3,%0\n"
       "add %3,%1\n"
-      "subl $2, %%ecx\n"
       "psubb %%mm2, %%mm0\n"
       "psubb %%mm3, %%mm1\n"
       "pxor %%mm7, %%mm0\n"
       "pxor %%mm7, %%mm1\n"
-      SUM(%%mm0, %%mm1, %%mm4, %%mm5)
+      "jmp 2f\n"
       "1:\n"
 
       SUM(%%mm4, %%mm5, %%mm0, %%mm1)
-
+      "2:\n"
       SUM(%%mm0, %%mm1, %%mm4, %%mm5)
 
       "subl $2, %%ecx\n"