tracing/eprobe: Fix alloc event dir failed when event name no set

tracing/eprobe: Fix alloc event dir failed when event name no set

The event dir will alloc failed when event name no set, using the
command:
"echo "e:esys/ syscalls/sys_enter_openat file=\$filename:string"
>> dynamic_events"
It seems that dir name="syscalls/sys_enter_openat" is not allowed
in debugfs. So just use the "sys_enter_openat" as the event name.

Link: https://lkml.kernel.org/r/1664028814-45923-1-git-send-email-chentao.kernel@linux.alibaba.com
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Linyu Yuan <quic_linyyuan@quicinc.com>
Cc: Tao Chen <chentao.kernel@linux.alibaba.com
Cc: stable@vger.kernel.org
Fixes: 95c104c378dc ("tracing: Auto generate event name when creating a group of events")
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Tao Chen <chentao.kernel@linux.alibaba.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>