Correct function signature for Visual Studio

- There would be VS build warning on unaligned formal parameter.

Change-Id: I6e122c4fec2505ef3458e4bdf218d3cd30bb494f

aom_dsp/x86/inv_txfm_common_avx2.h

@@ -71,8 +71,8 @@ static INLINE void unpack_butter_fly(const __m256i *a0, const __m256i *a1,
   __m256i x0, x1;
   x0 = _mm256_unpacklo_epi16(*a0, *a1);
   x1 = _mm256_unpackhi_epi16(*a0, *a1);
-  *b0 = butter_fly(x0, x1, *c0);
-  *b1 = butter_fly(x0, x1, *c1);
+  *b0 = butter_fly(&x0, &x1, c0);
+  *b1 = butter_fly(&x0, &x1, c1);
 }
 
 void av1_idct16_avx2(__m256i *in);

aom_dsp/x86/txfm_common_avx2.h

@@ -163,10 +163,11 @@ static INLINE void mm256_transpose_16x16(const __m256i *in, __m256i *out) {
   out[15] = _mm256_permute2x128_si256(tr0_7, tr0_f, 0x31);
 }
 
-static INLINE __m256i butter_fly(__m256i a0, __m256i a1, const __m256i cospi) {
+static INLINE __m256i butter_fly(const __m256i *a0, const __m256i *a1,
+                                 const __m256i *cospi) {
   const __m256i dct_rounding = _mm256_set1_epi32(DCT_CONST_ROUNDING);
-  __m256i y0 = _mm256_madd_epi16(a0, cospi);
-  __m256i y1 = _mm256_madd_epi16(a1, cospi);
+  __m256i y0 = _mm256_madd_epi16(*a0, *cospi);
+  __m256i y1 = _mm256_madd_epi16(*a1, *cospi);
 
   y0 = _mm256_add_epi32(y0, dct_rounding);
   y1 = _mm256_add_epi32(y1, dct_rounding);