alarmtimer: Remove unnecessary (void *) cast

Pointers of type void * do not require a type cast when they are assigned
to a real pointer.

Signed-off-by: Li zeming <zeming@nfschina.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230609182059.4509-1-zeming@nfschina.com