hw/mips/loongson3_virt: do not require CONFIG_USB

Once the Kconfig for hw/mips is cleaned up, it will be possible to build a
binary that does not include any USB host controller and therefore that
does not include the code guarded by CONFIG_USB.  While the simpler
creation functions such as usb_create_simple can be inlined, this is not
true of usb_bus_find().  Remove it, replacing it with a search of the
single USB bus created by loongson3_virt_devices_init().

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20240223124406.234509-5-pbonzini@redhat.com>
[PMD: Fixed style]
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

hw/mips/loongson3_virt.c

@@ -446,9 +446,13 @@ static inline void loongson3_virt_devices_init(MachineState *machine,
     pci_vga_init(pci_bus);
 
     if (defaults_enabled() && object_class_by_name("pci-ohci")) {
+        USBBus *usb_bus;
+
         pci_create_simple(pci_bus, -1, "pci-ohci");
-        usb_create_simple(usb_bus_find(-1), "usb-kbd");
-        usb_create_simple(usb_bus_find(-1), "usb-tablet");
+        usb_bus = USB_BUS(object_resolve_type_unambiguous(TYPE_USB_BUS,
+                                                          &error_abort));
+        usb_create_simple(usb_bus, "usb-kbd");
+        usb_create_simple(usb_bus, "usb-tablet");
     }
 
     pci_init_nic_devices(pci_bus, mc->default_nic);