libata-acpi: adjust constness in ata_acpi_gtm/stm() parameters
* No internal function uses const ata_port. Drop const from @ap.
* Make ata_acpi_stm() copy @stm before using it and change @stm to
const.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>