eighty_ninty_three() had word 93 validitity check but not the 80c bit
test itself (bit 13).  This increases the chance of incorrect wire
detection especially because host side cable detection is often
unreliable and we sometimes soley depend on drive side cable
detection.  Fix it.

[ bart: fix off-by-1 bit name in the patch description ]
Signed-off-by: Tejun Heo <htejun@gmail.com>
Acked-by: Alan Cox <alan@redhat.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>