Using VP9_FRAME_MARKER instead of raw number.

Change-Id: I3addbf6d89a86a707c8df1a463da3e9e367910df

vp9/vp9_dx_iface.c

@@ -160,7 +160,8 @@ static vpx_codec_err_t vp9_peek_si(const uint8_t         *data,
     struct vp9_read_bit_buffer rb = { data, data + data_sz, 0, NULL, NULL };
     const int frame_marker = vp9_rb_read_literal(&rb, 2);
     const int version = vp9_rb_read_bit(&rb) | (vp9_rb_read_bit(&rb) << 1);
-    if (frame_marker != 0x2) return VPX_CODEC_UNSUP_BITSTREAM;
+    if (frame_marker != VP9_FRAME_MARKER)
+      return VPX_CODEC_UNSUP_BITSTREAM;
 #if CONFIG_NON420
     if (version > 1) return VPX_CODEC_UNSUP_BITSTREAM;
 #else