ata: ahci_platform: correct parameter documentation for ahci_platform_shutdown

The documentation about parameter for ahci_platform_shutdown has a typo.

This fix the following build warning:
drivers/ata/libahci_platform.c:693: warning: Function parameter or member 'pdev' not described in 'ahci_platform_shutdown'
drivers/ata/libahci_platform.c:693: warning: Excess function parameter 'dev' description in 'ahci_platform_shutdow

Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>