sim: Use Option instead of Err<T, ()>
sim: Use Option instead of Err<T, ()>

Instead of using an Err type with no meaningful error type, just use an
Option.

Signed-off-by: David Brown <0af22db655f3ade5845314d695c1f4910314b0cb@linaro.org>

ATmobica/mcuboot,ATmobica/mcuboot,runtimeco/mcuboot,ATmobica/mcuboot,runtimeco/mcuboot,runtimeco/mcuboot,runtimeco/mcuboot,ATmobica/mcuboot,runtimeco/mcuboot,ATmobica/mcuboot