zephyr: Define an empty adc.h for now
While we wait for an ADC shim, define this enum so that the code at
least compiles.
BRANCH=none
TEST=build zephyr for volteer
#define ADC_READ_ERROR -1 /* Value returned by adc_read_channel() on error */
+#ifdef CONFIG_ZEPHYR
+/* TODO(b/175881324): Add a shim for ADC */
+enum adc_channel {
+ ADC_NONE,
+};
+#endif
+
/*
* Boards which use the ADC interface must provide enum adc_channel in the
* board.h file. See chip/$CHIP/adc_chip.h for additional chip-specific
