libata: fix ata_set_max_sectors()

In ata_set_max_sectors(), the highest nibble in LBA28 mode was
missing.  This made drives sized between 8G and 128G with HPA turned
on to be resized to under 8G.  Fix it.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>