atomic: Avoid casting the return value of atomic_load_ptr to void *

Otherwise a cast is needed to load a uintptr_t value.

Fixes: e1f4d623779d ("rangelocks: remove unneeded cast of the atomic_load_ptr() result")
MFC after: 1 week

(cherry picked from commit c7a7e997d25d0b33769252d002b16839c864c83d)