Fix warnings:

i386/vp3dsp_sse2.c:805: warning: cast discards qualifiers from pointer target type
i386/vp3dsp_sse2.c:806: warning: cast discards qualifiers from pointer target type

Originally committed as revision 12150 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/i386/vp3dsp_sse2.c

@@ -802,8 +802,8 @@ void ff_vp3_idct_sse2(int16_t *input_data)
 {
     unsigned char *input_bytes = (unsigned char *)input_data;
     unsigned char *output_data_bytes = (unsigned char *)input_data;
-    unsigned char *idct_data_bytes = (unsigned char *)SSE2_idct_data;
-    unsigned char *Eight = (unsigned char *)eight_data;
+    const unsigned char *idct_data_bytes = (const unsigned char *)SSE2_idct_data;
+    const unsigned char *Eight = (const unsigned char *)eight_data;
 
 #define eax input_bytes
 //#define ebx dequant_matrix_bytes