tracepoint: Optimize the critical region of mutex_lock in tracepoint_module_coming()

The memory allocation of 'tp_mod' does not require mutex_lock()
protection, move it out.

Link: https://lkml.kernel.org/r/20220914061416.1630-1-thunder.leizhen@huawei.com

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>