Don't wakeup the fdc worker thread once a second when idle.

The fdc worker thread was using a one second timeout while waiting for
a new bio to arrive or for the device to detach. However, the driver
already does a wakeup when queueing a new bio or asking the thread to
detach, so the timeout only served to waste CPU time waking up the
thread once a second just so it could go right back to sleep. Use an
infinite timeout instead.

Discussed with: phk
Sponsored by: Netflix