sensor_t is not always a valid name when compiling this against ESP8266/ESP32

[ggilestro]

This code will not work for me on the ESP8266 / ESP32 unless I rename all instances of sensor_t to something proprietary, like adafruit_sensor_t. I believe it is because of a clash with an existing piece of code for ESP32-Camera:

https://github.com/espressif/esp32-camera/blob/61400bc73b18e9ffcfd5b3806fee26d135c45fe7/driver/include/sensor.h#L189-L195