selftests/ftrace: Fix dependencies for some of the synthetic event tests

selftests/ftrace: Fix dependencies for some of the synthetic event tests

Commit b81a3a100cca1b ("tracing/histogram: Add simple tests for
stacktrace usage of synthetic events") changed the output text in
tracefs README, but missed updating some of the dependencies specified
in selftests. This causes some of the tests to exit as unsupported.

Fix this by changing the grep pattern. Since we want these tests to work
on older kernels, match only against the common last part of the
pattern.

Link: https://lore.kernel.org/linux-trace-kernel/20230614091046.2178539-1-naveen@kernel.org
Cc: <linux-kselftest@vger.kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Fixes: b81a3a100cca ("tracing/histogram: Add simple tests for stacktrace usage of synthetic events")
Signed-off-by: Naveen N Rao <naveen@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>