ftrace: Fix direct_functions leak in update_ftrace_direct_del

Alexei reported memory leak in update_ftrace_direct_del.
We miss cleanup of the replaced direct_functions in the
success path in update_ftrace_direct_del, adding that.

Fixes: 8d2c123 ("ftrace: Add update_ftrace_direct_del function")
Reported-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Closes: https://lore.kernel.org/bpf/aX_BxG5EJTJdCMT9@krava/T/#m7c13f5a95f862ed7ab78e905fbb678d635306a0c
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20260202075849.1684369-1-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: olsajiri

kernel/trace/ftrace.c

@@ -6537,6 +6537,7 @@ int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace_hash *hash)
 		/* free the new_direct_functions */
 		old_direct_functions = new_direct_functions;
 	} else {
+		old_direct_functions = direct_functions;
 		rcu_assign_pointer(direct_functions, new_direct_functions);
 	}