[libata] pata_legacy: for VLB 32bit PIO don't try tricks with slop

These devices are generally used with ATA anyway and it seems that some
ATAPI will need us to issue the right number of words.  Therefore as we
can't switch mid burst on VLB devices we should only use 32bit I/O for
suitable block sizes.

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>