bcachefs: Add distinct error code for key_cache_upgrade

This aids in debugging.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/btree_key_cache.c

@@ -417,7 +417,7 @@ int bch2_btree_path_traverse_cached(struct btree_trans *trans, struct btree_path
 		if (!path->locks_want &&
 		    !__bch2_btree_path_upgrade(trans, path, 1)) {
 			trace_transaction_restart_ip(trans->fn, _THIS_IP_);
-			ret = btree_trans_restart(trans, BCH_ERR_transaction_restart_upgrade);
+			ret = btree_trans_restart(trans, BCH_ERR_transaction_restart_key_cache_upgrade);
 			goto err;
 		}
 

fs/bcachefs/errcode.h

@@ -22,6 +22,7 @@
 	x(transaction_restart,	transaction_restart_would_deadlock)	\
 	x(transaction_restart,	transaction_restart_would_deadlock_write)\
 	x(transaction_restart,	transaction_restart_upgrade)		\
+	x(transaction_restart,	transaction_restart_key_cache_upgrade)	\
 	x(transaction_restart,	transaction_restart_key_cache_fill)	\
 	x(transaction_restart,	transaction_restart_key_cache_raced)	\
 	x(transaction_restart,	transaction_restart_key_cache_realloced)\