ACPI / PCI: Use ACPI_COMPANION() instead of ACPI_HANDLE()

The ACPI_HANDLE() macro evaluates ACPI_COMPANION() internally to
return the handle of the device's ACPI companion, so it is much
more straightforward and efficient to use ACPI_COMPANION()
directly to obtain the device's ACPI companion object instead of
using ACPI_HANDLE() and acpi_bus_get_device() on the returned
handle for the same thing.

Use ACPI_COMPANION() instead of ACPI_HANDLE() in the PCI ACPI support
code.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>