iidtx4_sse2: silence tran_high conv warning

cast Sqrt to short, _mm_set1_epi16 expects this as input

Change-Id: I667cd0bfcc86acfa5ccd7069f02e4dd1ec7b6bae

av1/common/x86/idct_intrin_sse2.c

@@ -356,7 +356,7 @@ static void iidtx8_sse2(__m128i *in) {
 }
 
 static INLINE void iidtx4_sse2(__m128i *in) {
-  const __m128i v_scale_w = _mm_set1_epi16(Sqrt2);
+  const __m128i v_scale_w = _mm_set1_epi16((int16_t)Sqrt2);
 
   const __m128i v_p0l_w = _mm_mullo_epi16(in[0], v_scale_w);
   const __m128i v_p0h_w = _mm_mulhi_epi16(in[0], v_scale_w);