Fix tracing sample code warning.

Commit 6575257c ("tracing/samples: Fix creation and deletion of
simple_thread_fn creation") introduced a new warning due to using a
boolean as a counter.

Just make it "int".

Fixes: 6575257c ("tracing/samples: Fix creation and deletion of simple_thread_fn creation")
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>