Fix mingw build for multicast.c

https://github.com/Hamlib/Hamlib/issues/695

src/multicast.c

@@ -326,11 +326,8 @@ void *multicast_thread(void *vrig)
 
 #ifdef WIN32
 static char *GetWinsockLastError(char *errorBuffer, DWORD errorBufferSize)
-{
-    void GetWinsockErrorString(char *errorBuffer, DWORD errorBufferSize)
 {
     int errorCode = WSAGetLastError();
-        DWORD charsWritten;
 
     FormatMessage(
         FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
@@ -341,6 +338,7 @@ static char *GetWinsockLastError(char *errorBuffer, DWORD errorBufferSize)
         errorBufferSize,
         NULL
     );
+    return errorBuffer;
 }
 #endif
 
@@ -483,11 +481,6 @@ static char *GetWinsockLastError(char *errorBuffer, DWORD errorBufferSize)
         rig_debug(RIG_DEBUG_ERR, "%s: sendto: %s\n", __func__, strerror(errno));
         return -RIG_EIO;
     }
-        else
-        {
-//        printf("Sent %zd bytes to multicast group %s:%d\n", num_bytes, MULTICAST_ADDR,
-//               PORT);
-        }
 
     return num_bytes;
 }