btrfs: add lockdep assertion to remaining delalloc callbacks

The merge and split callbacks for an inode's io tree are supposed to be
called while the io tree's spinlock is being held, so that the given
extent_state records are stable, not modified or freed while the callbacks
are using them. So add lockdep assertions in the callbacks.

Reviewed-by: Boris Burkov <boris@bur.io>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>