Revert "bootdev: avoid infinite probe loop"

Revert "bootdev: avoid infinite probe loop"

This turns out to be insufficient to fix the problem, since when
bootdev_next_prio() exits, the caller has no idea that this really
is the end. Nor is it, since there may be other devices which should
be checked.

The caller iterates which calls iter_incr() which calls
bootdev_next_prio() again, which finds the same device and the loop
continues.

We never did create a test for this[1], which makes it hard to be
sure which problem was fixed.

The original code had the virtue of staying in the loop looking for a
bootdev, so let's go back to that and try to fix this another way.

A future patch will make bootdev_next_prio() continue after failure
which should provide same effect.

This reverts commit 9d92c418acfb7576e12e2bd53fed294bb9543724.

Signed-off-by: Simon Glass <sjg@chromium.org>