tracing/perf: Use strndup_user instead of kzalloc/strncpy_from_user

This patch uses strndup_user instead of kzalloc + strncpy_from_user,
which makes the code more concise.

Link: https://lkml.kernel.org/r/20221121080831.707409-1-nashuiliang@gmail.com



Signed-off-by: Chuang Wang <nashuiliang@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>