Update adc.rst. Merges #1657

Author: superham

docs/api-reference/peripherals/adc.rst

@@ -6,7 +6,7 @@ Overview
 
 ESP32 integrates two 12-bit SAR (`Successive Approximation Register <https://en.wikipedia.org/wiki/Successive_approximation_ADC>`_) ADCs (Analog to Digital Converters) and supports measurements on 18 channels (analog enabled pins). Some of these pins can be used to build a programmable gain amplifier which is used for the measurement of small analog signals.
 
-The ADC driver API supports ADC1 (9 channels, attached to GPIOs 32 - 39), and ADC2 (10 channels, attached to GPIOs 0, 2, 4, 12 - 15 and 25 - 27).
+The ADC driver API supports ADC1 (8 channels, attached to GPIOs 32 - 39), and ADC2 (10 channels, attached to GPIOs 0, 2, 4, 12 - 15 and 25 - 27).
 However, there're some restrictions for the application to use ADC2:
 
 1. The application can use ADC2 only when Wi-Fi driver is not started, since the ADC is also used by the Wi-Fi driver, which has higher priority.