instead of when it goes above, do it precisely on the
timeout. otherwise, if by sheer chance the signal
pauses and we reset the byte - sure, ok, but it's a
bit tight and we run the risk of advancing another
frame, depending on the timing.
this is a minor edge case, probably rarely ever
triggered in practise.
Signed-off-by: Leah Rowe <leah@libreboot.org>