tick-sched: Clarify "NOHZ: local_softirq_pending" warning

Currently, can_stop_idle_tick() prints "NOHZ: local_softirq_pending HH"
(where "HH" is the hexadecimal softirq vector number) when one or more
non-RCU softirq handlers are still enabled when checking to stop the
scheduler-tick interrupt.  This message is not as enlightening as one
might hope, so this commit changes it to "NOHZ tick-stop error: Non-RCU
local softirq work is pending, handler #HH".

Reported-by: Andy Lutomirski <luto@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>