dsputil: mark source of diff_bytes as const.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/dsputil.c

@@ -1921,7 +1921,7 @@ static void add_bytes_c(uint8_t *dst, uint8_t *src, int w){
         dst[i+0] += src[i+0];
 }
 
-static void diff_bytes_c(uint8_t *dst, uint8_t *src1, uint8_t *src2, int w){
+static void diff_bytes_c(uint8_t *dst, const uint8_t *src1, const uint8_t *src2, int w){
     long i;
 #if !HAVE_FAST_UNALIGNED
     if((long)src2 & (sizeof(long)-1)){

libavcodec/dsputil.h

@@ -378,7 +378,7 @@ typedef struct DSPContext {
 
     /* huffyuv specific */
     void (*add_bytes)(uint8_t *dst/*align 16*/, uint8_t *src/*align 16*/, int w);
-    void (*diff_bytes)(uint8_t *dst/*align 16*/, uint8_t *src1/*align 16*/, uint8_t *src2/*align 1*/,int w);
+    void (*diff_bytes)(uint8_t *dst/*align 16*/, const uint8_t *src1/*align 16*/, const uint8_t *src2/*align 1*/,int w);
     /**
      * subtract huffyuv's variant of median prediction
      * note, this might read from src1[-1], src2[-1]

libavcodec/x86/dsputilenc_mmx.c

@@ -821,7 +821,7 @@ static int vsad16_mmx2(void *v, uint8_t * pix1, uint8_t * pix2, int line_size, i
 }
 #undef SUM
 
-static void diff_bytes_mmx(uint8_t *dst, uint8_t *src1, uint8_t *src2, int w){
+static void diff_bytes_mmx(uint8_t *dst, const uint8_t *src1, const uint8_t *src2, int w){
     x86_reg i=0;
     __asm__ volatile(
         "1:                             \n\t"