null_blk: Switch to use hrtimer_setup()

null_blk: Switch to use hrtimer_setup()

hrtimer_setup() takes the callback function pointer as argument and
initializes the timer completely.

Replace hrtimer_init() and the open coded initialization of
hrtimer::function with the new setup mechanism.

Patch was created by using Coccinelle.

Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/076cd30acb4b2d6b699f3c80463a8983530d4f06.1738746821.git.namcao@linutronix.de