bcachefs: Improve error printing in btree_node_check_topology()

bcachefs: Improve error printing in btree_node_check_topology()

We had a bug report where the errors from btree_node_check_topology()
don't seem to be getting printed; log_fsck_err() does some fancy
ratelimiting-type stuff that we don't want here.

Instead, just use bch2_count_fsck_err(); this is simpler, and modelled
after how we're currently handling bucket ref update errors in
buckets.c.

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