hw/usb/Kconfig: USB_XHCI_NEC requires USB_XHCI

TYPE_NEC_XHCI is child of TYPE_XHCI. Add the missing Kconfig
dependency.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/usb/Kconfig

@@ -40,7 +40,7 @@ config USB_XHCI_NEC
     bool
     default y if PCI_DEVICES
     depends on PCI
-    select USB
+    select USB_XHCI
 
 config USB_MUSB
     bool