If SCSI commands are submitted while other commands are still processed,
the dispatch loop turns, and we stop the work_timer. Then, if URB fails
to complete, ub hangs until the device is unplugged.

This does not happen often, becase we only allow one SCSI command per
block device, but does happen (on multi-LUN devices, for example).

The fix is to stop timer only when we actually going to change the state.

The nicest code would be to have the timer stopped in URB callback, but
this is impossible, because it can be called from inside a timer, through
the urb_unlink. Then we get BUG in timer.c:cascade(). So, we do it a
little dirtier.

Signed-off-by: Pete Zaitcev <zaitcev@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>