fs: Make wbc_to_tag() inline and use it in fs.

fs: Make wbc_to_tag() inline and use it in fs.

The logic in wbc_to_tag() is widely used in file systems, so modify this
function to be inline and use it in file systems.

This patch has only passed compilation tests, but it should be fine.

Signed-off-by: Julian Sun <sunjunchao@bytedance.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>