time/jiffies: Change register_refined_jiffies() to void __init

register_refined_jiffies() is only used in setup code and always returns 0.
Mark it as __init to save some bytes and change it to void.

Signed-off-by: Su Hui <suhui@nfschina.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250430032734.2079290-2-suhui@nfschina.com