timers: Add sparse annotation for timer_sync_wait_running().

timer_sync_wait_running() first releases two locks and then acquires
them again. This is unexpected and sparse complains about it.

Add sparse annotation for timer_sync_wait_running() to note that the
locking is expected.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240812105326.2240000-2-bigeasy@linutronix.de