bcachefs: Avoid using btree_node_lock_nopath()

bcachefs: Avoid using btree_node_lock_nopath()

With the upcoming cycle detector, we have to be careful about using
btree_node_lock_nopath - in particular, using it to take write locks can
cause deadlocks.

All held locks need to be tracked in a btree_path, so that the cycle
detector knows about them - unless we know that we cannot cause
deadlocks for other reasons: e.g. we are only taking read locks, or
we're in very early fsck (topology repair).

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>