tracing/timer: Add missing argument documentation of trace points

Documentation of trace points timer_start, timer_expire_entry and
hrtimer_start lack always the last argument. Add it to keep implementation
and documentation in sync.

Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20220411140115.24185-1-anna-maria@linutronix.de