Fix copy-and-paste error in comment for RGB to YUV
The comment should say AVIF_CHROMA_DOWNSAMPLING_xxx, not
AVIF_CHROMA_UPSAMPLING_xxx.
diff --git a/include/avif/avif.h b/include/avif/avif.h
index 5800b33..9b34159 100644
--- a/include/avif/avif.h
+++ b/include/avif/avif.h
@@ -547,7 +547,7 @@
//
// * YUV depth: 8
// * RGB depth: 8
-// * rgb.chromaDownsampling: AVIF_CHROMA_UPSAMPLING_AUTOMATIC, AVIF_CHROMA_UPSAMPLING_FASTEST
+// * rgb.chromaDownsampling: AVIF_CHROMA_DOWNSAMPLING_AUTOMATIC, AVIF_CHROMA_DOWNSAMPLING_FASTEST
// * One of the following combinations (avifRGBFormat to avifPixelFormat/MC/Range):
// * BGRA to YUV400 / x /[Full|Limited]
// * BGRA to [YUV420|YUV422]/[5|6]/[Full|Limited]