resize_avx2.c: fix integer sanitizer conversion warning

add missing cast in call to _mm256_set1_epi8().

fixes:
implicit conversion from type 'uint8_t' (aka 'unsigned char') of value
255 (8-bit, unsigned) to type 'char' changed the value to -1 (8-bit,
signed)

Change-Id: I9bf7a217f650a7255ed35ab7075358cb5e8e14d8
diff --git a/av1/common/x86/resize_avx2.c b/av1/common/x86/resize_avx2.c
index c44edb8..47f015a 100644
--- a/av1/common/x86/resize_avx2.c
+++ b/av1/common/x86/resize_avx2.c
@@ -174,7 +174,7 @@
   const __m128i round_shift_bits = _mm_cvtsi32_si128(bits);
   const __m256i round_const_bits = _mm256_set1_epi32((1 << bits) >> 1);
   const uint8_t max_pixel = 255;
-  const __m256i clip_pixel = _mm256_set1_epi8(max_pixel);
+  const __m256i clip_pixel = _mm256_set1_epi8((char)max_pixel);
   const __m256i zero = _mm256_setzero_si256();
 
   prepare_filter_coeffs(av1_down2_symeven_half_filter, coeffs_y);