ftrace: Use this_cpu_ptr() instead of per_cpu_ptr(smp_processor_id())

Use this_cpu_ptr() instead of open coding the equivalent in various
ftrace functions.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/87y14t6ofi.wl-me@linux.beauty


Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>