Merge branch 'bugfix/compilation_warnings' into 'master'

bugfix/compilation_warnings: Fixes minor compilation warnings

See merge request sdk/ESP8266_RTOS_SDK!794

Author: donghengqaz

components/esp8266/driver/adc.c

@@ -25,7 +25,6 @@
 #define ENTER_CRITICAL() portENTER_CRITICAL()
 #define EXIT_CRITICAL() portEXIT_CRITICAL()
 
-static const char *TAG = "adc";
 
 #define ADC_CHECK(a, str, ret_val) \
     if (!(a)) { \

components/mqtt/paho/MQTTClient-C/src/FreeRTOS/MQTTFreeRTOS.c

@@ -70,7 +70,7 @@ void TimerCountdown(Timer *timer, unsigned int timeout)
 int TimerLeftMS(Timer *timer)
 {
     xTaskCheckForTimeOut(&timer->xTimeOut, &timer->xTicksToWait); /* updates xTicksToWait to the number left */
-    return (timer->xTicksToWait < 0) ? 0 : (timer->xTicksToWait * portTICK_PERIOD_MS);
+    return (timer->xTicksToWait <= 0) ? 0 : (timer->xTicksToWait * portTICK_PERIOD_MS);
 }