tick/sched: Fix struct tick_sched doc warnings

Fix kernel-doc warnings in struct tick_sched:

  tick-sched.h:103: warning: Function parameter or struct member 'idle_sleeptime_seq' not described in 'tick_sched'
  tick-sched.h:104: warning: Excess struct member 'nohz_mode' description in 'tick_sched'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240331172652.14086-6-rdunlap@infradead.org