lib: test_objpool: Switch to use hrtimer_setup()

lib: test_objpool: 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/edc46fbf290b280ebe67bb0d21599c4c30716b68.1738746821.git.namcao@linutronix.de