video_core: fix build on Apple Clang

src/video_core/texture_cache/texture_cache.h

@@ -888,7 +888,7 @@ void TextureCache<P>::DownloadImageIntoBuffer(typename TextureCache<P>::Image* i
             buffer,
             download_map.buffer,
         };
-        std::array buffer_offsets{
+        std::array<u64, 2> buffer_offsets{
             buffer_offset,
             download_map.offset,
         };