fomu: bsp: don't call usb isr when usb is disabled

When compiled without usb support, we don't want to call the USB ISR.

Signed-off-by: Sean Cross <sean@xobs.io>

hw/bsp/fomu/fomu.c

@@ -63,9 +63,11 @@ void isr(void)
 
   irqs = irq_pending() & irq_getmask();
 
+#if CFG_TUSB_RHPORT0_MODE == OPT_MODE_DEVICE
   if (irqs & (1 << USB_INTERRUPT)) {
     hal_dcd_isr(0);
   }
+#endif
   if (irqs & (1 << TIMER0_INTERRUPT)) {
     system_ticks++;
     timer0_ev_pending_write(1);