ASoC: tas2770: Deal with bogus initial temperature value

ASoC: tas2770: Deal with bogus initial temperature value

TAS2770 initialises the temperature readout registers to 0.
This value persists until the chip is fully powered up and
the ADC starts sampling. The ADC then persists the last sampled
temperature during software shutdown.

The ADC should therefore never return 0 in normal operating
conditions, so return -ENODATA and mark it as a fault condition
using HWMON_T_FAULT.

Fixes: ff73e2780169 ("ASoC: tas2770: expose die temp to hwmon")
Signed-off-by: James Calligeros <jcalligeros99@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>