rp2040: fix interrupt issue

src/machine/machine_rp2040_usb.go

@@ -101,6 +101,7 @@ func handleUSBIRQ(intr interrupt.Interrupt) {
 		}
 
 		s2 := rp.USBCTRL_REGS.BUFF_STATUS.Get()
+		rp.USBCTRL_REGS.BUFF_STATUS.Set(s2)
 
 		// OUT (PC -> rp2040)
 		for i := 0; i < 16; i++ {
@@ -121,8 +122,6 @@ func handleUSBIRQ(intr interrupt.Interrupt) {
 				}
 			}
 		}
-
-		rp.USBCTRL_REGS.BUFF_STATUS.Set(0xFFFFFFFF)
 	}
 
 	// Bus is reset