ich6_sata_ahci and ich6_sata are identical.  Kill ich6_sata_ahci and
drop _ahci postfixes from controller ids, which doesn't really mean
anything at this point.
Signed-off-by: NTejun Heo <htejun@gmail.com>
Signed-off-by: NJeff Garzik <jeff@garzik.org>