selftests/ftrace: fix dynamic_events dependency check

commit 95c104c3 ("tracing: Auto generate event name when creating a
group of events") changed the syntax in the ftrace README file which is
used by the selftests to check what features are support. Adjust the
string to make test_duplicates.tc and trigger-synthetic-eprobe.tc work
again.

Fixes: 95c104c3 ("tracing: Auto generate event name when creating a group of events")
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>