bcachefs: Don't decrease BTREE_ITER_MAX when LOCKDEP=y

bcachefs: Don't decrease BTREE_ITER_MAX when LOCKDEP=y

Running with fewer max btree paths doesn't work anymore when replication
is enabled - as we've added e.g. the freespace and bucket gens btrees,
we naturally end up needing more btree paths.

This is an issue with lockdep, we end up taking more locks than lockdep
will track (the MAX_LOCKD_DEPTH constant). But bcachefs as merged does
not yet support lockdep anyways, so we can leave that for later.

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