hw/acpi: use existing references to pci device struct within functions

hw/acpi: use existing references to pci device struct within functions

There is no need to use fresh typecasts to get references to pci device structs
when there is an existing reference to pci device struct. Use existing reference.
Minor cleanup.

Signed-off-by: Ani Sinha <ani@anisinha.ca>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210825031949.919376-3-ani@anisinha.ca>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>