Documentation: core-api/cpuhotplug: Fix state names

Dynamic allocated hotplug states in documentation and the comment above
cpuhp_state enum do not match the code. To not get confused by wrong
documentation, change to proper state names.

Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230515162038.62703-1-anna-maria@linutronix.de