Fix SPLIT_KEYBOARD compilation for ATMega*U2, which doesn't have VBUS/OTG control (#10460)

Co-authored-by: s-ol <s-ol@users.noreply.github.com>

quantum/split_common/split_util.c

@@ -72,7 +72,7 @@ bool usbIsActive(void) {
 
     return false;
 }
-#elif defined(PROTOCOL_LUFA)
+#elif defined(PROTOCOL_LUFA) && defined(OTGPADE)
 static inline bool usbIsActive(void) {
     USB_OTGPAD_On();  // enables VBUS pad
     wait_us(5);