ppc: add const where needed in scalarproduct_int16_altivec()

Signed-off-by: Mans Rullgard <mans@mansr.com>

libavcodec/ppc/int_altivec.c

@@ -79,17 +79,18 @@ static int ssd_int8_vs_int16_altivec(const int8_t *pix1, const int16_t *pix2,
     return u.score[3];
 }
 
-static int32_t scalarproduct_int16_altivec(int16_t *v1, const int16_t *v2,
+static int32_t scalarproduct_int16_altivec(const int16_t *v1, const int16_t *v2,
                                            int order)
 {
     int i;
     LOAD_ZERO;
-    register vec_s16 vec1, *pv;
+    const vec_s16 *pv;
+    register vec_s16 vec1;
     register vec_s32 res = vec_splat_s32(0), t;
     int32_t ires;
 
     for(i = 0; i < order; i += 8){
-        pv = (vec_s16*)v1;
+        pv = (const vec_s16*)v1;
         vec1 = vec_perm(pv[0], pv[1], vec_lvsl(0, v1));
         t = vec_msum(vec1, vec_ld(0, v2), zero_s32v);
         res = vec_sums(t, res);