btrfs: use write_extent_buffer() to implement write_extent_buffer_*id()

Helpers write_extent_buffer_chunk_tree_uuid() and
write_extent_buffer_fsid(), they can be implemented by
write_extent_buffer().

These two helpers are not that frequently used, they only get called
during initialization of a new tree block.  There is not much need for
those slightly optimized versions.  And since they can be easily
converted to one write_extent_buffer() call, define them as inline
helpers.

This would make later page/folio switch much easier, as all change only
need to happen in write_extent_buffer().

Reviewed-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>