vpx_dsp/x86/highbd_idct4x4_add_sse2: fix int sanitizer warnings

implicit conversion from type 'int' of value 49161 (32-bit, signed) to
type 'int16_t' (aka 'short') changed the value to -16375 (16-bit,
signed)

BUG=webm:1615

Change-Id: I3f18283609ac2ce365202a63ef61a47eb00c155b
diff --git a/vpx_dsp/x86/highbd_idct4x4_add_sse2.c b/vpx_dsp/x86/highbd_idct4x4_add_sse2.c
index 2e54d24..b9c8884 100644
--- a/vpx_dsp/x86/highbd_idct4x4_add_sse2.c
+++ b/vpx_dsp/x86/highbd_idct4x4_add_sse2.c
@@ -112,8 +112,8 @@
     min_input = _mm_min_epi16(min_input, _mm_srli_si128(min_input, 4));
     max_input = _mm_max_epi16(max_input, _mm_srli_si128(max_input, 2));
     min_input = _mm_min_epi16(min_input, _mm_srli_si128(min_input, 2));
-    max = _mm_extract_epi16(max_input, 0);
-    min = _mm_extract_epi16(min_input, 0);
+    max = (int16_t)_mm_extract_epi16(max_input, 0);
+    min = (int16_t)_mm_extract_epi16(min_input, 0);
   }
 
   if (bd == 8 || (max < 4096 && min >= -4096)) {