Fix PPC crash

Because of a typo, structure field vga_bios_size was not initialized
properly and a bogus BAR6 for the nonexistent VGA BIOS appeared.

The bug was uncovered by c1699988.
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

hw/vga-pci.c

@@ -119,7 +119,7 @@ int pci_vga_init(PCIBus *bus,
 
     dev = pci_create(bus, -1, "VGA");
     qdev_prop_set_uint32(&dev->qdev, "bios-offset", vga_bios_offset);
-    qdev_prop_set_uint32(&dev->qdev, "bios-size", vga_bios_offset);
+    qdev_prop_set_uint32(&dev->qdev, "bios-size", vga_bios_size);
     qdev_init_nofail(&dev->qdev);
 
     return 0;