bcachefs: Make btree_iter_peek_prev() assert more precise

The issue this assert is guarding against is that in
BTREE_ITER_filter_snapshots mode we only want to be iterating within a
single inode number - if we iterate into another inode number with keys
for a different snapshot tree, we'll loop arbitrarily long before
finding a key we can return.

This comes up in the unit tests, where we're using inode 0 for our test
keys.

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

Author: Kent Overstreet

fs/bcachefs/btree_iter.c

@@ -2602,7 +2602,7 @@ struct bkey_s_c bch2_btree_iter_peek_prev_min(struct btree_trans *trans, struct
 
 	bch2_trans_verify_not_unlocked_or_in_restart(trans);
 	bch2_btree_iter_verify_entry_exit(iter);
-	EBUG_ON((iter->flags & BTREE_ITER_filter_snapshots) && bpos_eq(end, POS_MIN));
+	EBUG_ON((iter->flags & BTREE_ITER_filter_snapshots) && iter->pos.inode != end.inode);
 
 	int ret = trans_maybe_inject_restart(trans, _RET_IP_);
 	if (unlikely(ret)) {