libata fixes for sparse-found problems

In pata_legacy and pata_winbond we've got bugs - cpu_to_le16() instead
of cpu_to_le32().  Fortunately, both affected suckers are VLB, thus
l-e-only, so we might get away with that unless we hit it with slop == 3
(hadn't checked if playing with badly aligned sg could trigger that).
Still buggy...  Moreover, pata_legacy, pata_winbond and pata_qdi forgot to
initialize pad on the write side of 32bit case in their ->data_xfer().
Hopefully the hardware does't care, but still, sending uninitialized
data to it...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jeff Garzik <jeff@garzik.org>