ambiguous millis() function (with MQTT direct ESP Home added function)

[fabikm]

The error is related to the ambiguous millis() function due to the fact that there are different definitions of this function in the code. We can solve this problem by using a specific notation of the function so that the compiler knows which version to use.

For example:
Instead of millis(), use esphome::millis() if we will refer a function defined in ESPHome.

[krasa]

#18