RESEND: libata: check cdb len per dev instead of per host

Resending, with s/printk/DPRINTK/ as pointed out by Alan.

Fix libata to perform CDB len validation per device
rather than per host.  This way, validation still works
when we have a mix of 12-byte and 16-byte devices on
a common host interface.

Signed-off-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>