Abstract 5 identical code blocks into a readdisksector() function. Cleaner, clearer and less error prone.
Abstract 5 identical code blocks into a readdisksector() function.
Cleaner, clearer and less error prone.

Tested by bmercer@ as part of a larger diff, of which this is the
last part.

reads ok to jsing@ kettenis@. ok deraadt@.

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars