usb: fix usb-host dependency check

Fixes: 90540f32 ("configure, meson: convert libusb detection to meson", 2021-06-25)
Reported-by: Programmingkid <programmingkidx@gmail.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-Id: <20210721081718.301343-1-kraxel@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/usb/meson.build

@@ -72,7 +72,7 @@ if usbredir.found()
 endif
 
 # usb pass-through
-if config_host.has_key('CONFIG_USB_LIBUSB')
+if libusb.found()
   usbhost_ss = ss.source_set()
   usbhost_ss.add(when: ['CONFIG_USB', libusb],
                  if_true: files('host-libusb.c'))