doc: fix a broken link in fs.md

PR-URL: #31373
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Richard Lau <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Trivikram Kamat <[email protected]>
Reviewed-By: Daijiro Wachi <[email protected]>
Reviewed-By: Tobias Nießen <[email protected]>
Reviewed-By: Rich Trott <[email protected]>

Author: himself65

doc/api/fs.md

@@ -5588,4 +5588,4 @@ the file contents.
 [chcp]: https://ss64.com/nt/chcp.html
 [inode]: https://en.wikipedia.org/wiki/Inode
 [support of file system `flags`]: #fs_file_system_flags
-[Writable Stream]: #stream_class_stream_writable
+[Writable Stream]: stream.html#stream_class_stream_writable