machine: fix usb truncation?

Remove the sendUSBPacket maxLen param because this greatly confused the compiler.
It also fixes a bug where the length provided to the hardware may not match the length of the packet.
sendUSBPacket now panics if the sent packet is too big.

I also fixed some of the string descriptor logic where we could create a packet without fully populating it.

RP2* systems might require some more work since they are implemented very differently?
I don't have any of those to test with yet, so maybe someone can deal with them in a seperate PR?

src/machine/machine_rp2_usb.go

@@ -72,19 +72,15 @@ func initEndpoint(ep, config uint32) {
 
 // SendUSBInPacket sends a packet for USB (interrupt in / bulk in).
 func SendUSBInPacket(ep uint32, data []byte) bool {
-	sendUSBPacket(ep, data, 0)
+	sendUSBPacket(ep, data)
 	return true
 }
 
 // Prevent file size increases: https://github.com/tinygo-org/tinygo/pull/998
 //
 //go:noinline
-func sendUSBPacket(ep uint32, data []byte, maxsize uint16) {
+func sendUSBPacket(ep uint32, data []byte) {
 	count := len(data)
-	if 0 < int(maxsize) && int(maxsize) < count {
-		count = int(maxsize)
-	}
-
 	if ep == 0 {
 		if count > usb.EndpointPacketSize {
 			count = usb.EndpointPacketSize
@@ -145,7 +141,7 @@ func setEPDataPID(ep uint32, dataOne bool) {
 }
 
 func SendZlp() {
-	sendUSBPacket(0, []byte{}, 0)
+	sendUSBPacket(0, []byte{})
 }
 
 func sendViaEPIn(ep uint32, data []byte, count int) {