- __div64_32(): remove __attribute_pure__ qualifier from the prototype
   since this function obviously clobbers memory through &(n);

 - do_div(): add a check to ensure (n) is type-compatible with uint64_t;

 - as_update_iohist(): Use sector_div() instead of do_div().
   (Whether the result of the addition should always be stored in 64bits
   regardless of CONFIG_LBD is still being discussed, therefore it's
   unadderessed here);

 - Fix all places where do_div() was being called with a bad divisor argument.