selftests/ftrace: Change synthetic event name for inter-event-combined test

This test uses waking+wakeup_latency as an event name, which doesn't
make sense since it includes an operator.  Illegal names are now
detected by the synthetic event command parsing, which causes this
test to fail.  Change the name to 'waking_plus_wakeup_latency' to
prevent this.

Link: https://lkml.kernel.org/r/a1ee2f76ff28ef7166fb788ca8be968887808920.1602598160.git.zanussi@kernel.org

Fixes: f06eec4d

 (selftests: ftrace: Add inter-event hist triggers testcases)
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>