Renamed "ipPortUser_" to "ipPortAsynOctetSyncIO_"

I learned that there might be multiple asynUsers connected to the same
port for different types (asynInt32, asynOctet, ...). Therefore I
renamed "ipPortUser_" to better reflect this.

src/sinqAxis.cpp

@@ -662,8 +662,7 @@ extern "C" {
  */
 asynStatus setWatchdogEnabled(const char *portName, int axisNo, int enable) {
 
-    sinqController *pC;
-    pC = (sinqController *)findAsynPortDriver(portName);
+    sinqController *pC = (sinqController *)findAsynPortDriver(portName);
     if (pC == nullptr) {
         errlogPrintf("Controller \"%s\" => %s, line %d:\nPort %s not found.",
                      portName, __PRETTY_FUNCTION__, __LINE__, portName);