Treat zero xfer length as HSM violation.  While at it, add
unlikely()'s to ATAPI ireason and transfer length checks.

tj: Formatted patch and added unlikely()'s.
Signed-off-by: Albert Lee <albertcc@tw.ibm.com>
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>