Fix watchdog trigger timer. Kick the watchdog each 10 seconds.

Author: pennam

src/utility/spi_drv.cpp

@@ -217,12 +217,13 @@ void SpiDrv::waitForSlaveSign()
 
 void SpiDrv::waitForSlaveReady(bool const feed_watchdog)
 {
-    unsigned long const start = millis();
+    unsigned long trigger_time = millis() + 10000;
 	while (!waitSlaveReady())
     {
         if (feed_watchdog) {
-            if ((millis() - start) < 10000) {
+            if (static_cast<int32_t>(trigger_time - millis()) <=0) {
                 WiFi.feedWatchdog();
+                trigger_time = millis() + 10000;
             }
         }
     }