tracing: probeevent: Do not accumulate on ret variable

Do not accumulate strlen result on "ret" local variable, because
it is accumulated on "total" local variable for array case.

Link: http://lkml.kernel.org/r/155723735237.9149.3192150444705457531.stgit@devnote2



Fixes: 40b53b77 ("tracing: probeevent: Add array type support")
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>