Documentation: core-api/cpuhotplug: Fix missing prefix

Add the missing cpuhp_ prefix in cpuhp_remove_multi_state().

Signed-off-by: Lucas De Marchi <[e-mail]>
Signed-off-by: Jonathan Corbet <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/core-api/cpu_hotplug.rst

···
    ....
    cpuhp_remove_instance(state, &inst2->node);
    ....
-   remove_multi_state(state);
+   cpuhp_remove_multi_state(state);
 
 
 Testing of hotplug states