selftests/tracing: Fix event filter test to retry up to 10 times

selftests/tracing: Fix event filter test to retry up to 10 times

Commit eb50d0f250e9 ("selftests/ftrace: Choose target function for filter
test from samples") choose the target function from samples, but sometimes
this test failes randomly because the target function does not hit at the
next time. So retry getting samples up to 10 times.

Fixes: eb50d0f250e9 ("selftests/ftrace: Choose target function for filter test from samples")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>