ata: ahci: Convert __ahci_port_base to accepting hpriv as arguments

The port base address may be required even before the ata_host instance is
initialized and activated, for instance in the ahci_save_initial_config()
method which we are about to update (consider this modification as a
preparation for that one). Seeing the __ahci_port_base() function isn't
used much it's the best candidate to provide the required functionality.
So let's convert it to accepting the ahci_host_priv structure pointer.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>