ftrace: Add cleanup to unregister_ftrace_direct_multi

Adding ops cleanup to unregister_ftrace_direct_multi,
so it can be reused in another register call.

Link: https://lkml.kernel.org/r/20211206182032.87248-3-jolsa@kernel.org



Cc: Ingo Molnar <mingo@redhat.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Fixes: f64dd462 ("ftrace: Add multi direct register/unregister interface")
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>