hw/i386/pc_{piix, q35}: Eliminate local pci_bus/pci_host variables

hw/i386/pc_{piix, q35}: Eliminate local pci_bus/pci_host variables

There is no advantage in having these local variables which 1/ needlessly have
different identifiers in both machines and 2/ which are redundant to pcms->bus
which is almost as short.

Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Message-ID: <20240224135851.100361-4-shentey@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>