atomic: Fix the cast in the atomic_load_consume() interceptor

As in commit c7a7e997d25d0, we should permit loading from a pointer to
uintptr_t.

Note that the other atomic_*_ptr() interfaces currently require casting
regardless, only those defined in atomic_common.h try to be generic.

Reported by: jrtc27
MFC after: 1 week

(cherry picked from commit cb91dc50950ffdfd49337e844e231b69b8b5c634)