ata: ahci_xgene: free structure returned by acpi_get_object_info()

acpi_get_object_info() allocates the returned structure, which the
caller has to free when the call succeeds.  Free it when appropriate.

Fixes: c9802a4b ("ata: ahci_xgene: Add AHCI Support for 2nd HW version of APM X-Gene SoC AHCI SATA Host controller.")
Signed-off-by: Michał Kępień <kernel@kempniu.pl>
Signed-off-by: Tejun Heo <tj@kernel.org>