[PATCH] udev: sleep_for_dev() bits

OK, I fixed that bug you hinted at earlier in my previous
sleep_for_dev() patch.  I am sure you fixed it, but here we go
nonetheless, just in case.

I actually changed it up a bit.  It is probably faster to count down
from SECONDS_TO_WAIT_FOR_DEV than count up.

I also made the lone 'path' argument const, since it can be.

Some other misc. bits, too.