tracing: Change "char *" string form to "char []"

The "char []" string form declares a single variable. It is better
than "char *" which creates two variables in the final assembly.

Link: https://lkml.kernel.org/r/20220512143230.28796-1-liqiong@nfschina.com



Signed-off-by: liqiong <liqiong@nfschina.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>