dont trash mm0, its still used in the next iteration of the loop (fixes...

dont trash mm0, its still used in the next iteration of the loop (fixes strange horizontal lines on some blocks in b frames on mmx only cpus)

Originally committed as revision 855 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/i386/dsputil_mmx_rnd.h

@@ -214,10 +214,10 @@ static void DEF(avg, pixels_y2)(UINT8 *block, const UINT8 *pixels, int line_size
 	"movq	(%1, %%eax), %%mm0	\n\t"
 	PAVGBP(%%mm1, %%mm2, %%mm4,   %%mm0, %%mm1, %%mm5)
 	"movq	(%2), %%mm3		\n\t"
-	PAVGB(%%mm3, %%mm4, %%mm0, %%mm6)
+	PAVGB(%%mm3, %%mm4, %%mm2, %%mm6)
 	"movq	(%2, %3), %%mm3		\n\t"
 	PAVGB(%%mm3, %%mm5, %%mm1, %%mm6)
-	"movq	%%mm0, (%2)		\n\t"
+	"movq	%%mm2, (%2)		\n\t"
 	"movq	%%mm1, (%2, %3)		\n\t"
 	"addl	%%eax, %1		\n\t"
 	"addl	%%eax, %2		\n\t"