floppy: initialize debug jiffies offset

Set debug jiffies offset at initialization.  Avoids wierd values showing
up if debugging enabled.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>