ata: ahci_tegra: call tegra_powergate_power_off only when PM domain is not present

This patch adds check to call legacy power domain API
tegra_powergate_power_off() only when PM domain is not present.

Fixes: 868ed731 ("ata: ahci_tegra: Add AHCI support for Tegra186")
Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/1617915315-13639-2-git-send-email-skomatineni@nvidia.com


Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>