ata: libahci: Don't read AHCI version twice in the save-config method

There is no point in reading the AHCI version all over in the tail of the
ahci_save_initial_config() method. That register is RO and doesn't change
its value even after reset. So just reuse the data, which has already been
read from there earlier in the head of the function.

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>