hw/pci/pci.c: Use memory_region_init_rom()

hw/pci/pci.c: Use memory_region_init_rom()

Since we pass the same DeviceState object to
memory_region_init_rom_nomigrate() and vmstate_register_ram(), we can
switch to using memory_region_init_rom() instead.

(This isn't entirely obvious from the code since it is using
&pdev->qdev rather than DEVICE(pdov) for some reason, but
PCIDevice does indeed use 'qdev' for its parent DeviceState member.)

Signed-off-by: Peter Maydell <[email protected]>
Reviewed-by: Paolo Bonzini <[email protected]>
Message-id: 1499438577[email protected]