hw/pci-host/q35: Inline sysbus_add_io()

sysbus_add_io() just wraps memory_region_add_subregion() while also
obscuring where the memory is attached. So use
memory_region_add_subregion() directly and attach it to the existing
memory region s->mch.address_space_io which is set as an alias to
get_system_io() by the q35 machine.

Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20230213162004.2797-3-shentey@gmail.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/pci-host/q35.c

@@ -50,10 +50,12 @@ static void q35_host_realize(DeviceState *dev, Error **errp)
     Q35PCIHost *s = Q35_HOST_DEVICE(dev);
     SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
 
-    sysbus_add_io(sbd, MCH_HOST_BRIDGE_CONFIG_ADDR, &pci->conf_mem);
+    memory_region_add_subregion(s->mch.address_space_io,
+                                MCH_HOST_BRIDGE_CONFIG_ADDR, &pci->conf_mem);
     sysbus_init_ioports(sbd, MCH_HOST_BRIDGE_CONFIG_ADDR, 4);
 
-    sysbus_add_io(sbd, MCH_HOST_BRIDGE_CONFIG_DATA, &pci->data_mem);
+    memory_region_add_subregion(s->mch.address_space_io,
+                                MCH_HOST_BRIDGE_CONFIG_DATA, &pci->data_mem);
     sysbus_init_ioports(sbd, MCH_HOST_BRIDGE_CONFIG_DATA, 4);
 
     /* register q35 0xcf8 port as coalesced pio */