If the thermal core tries to update the temperature from an
uninitialized power supply, it will swawn the following warning:
thermal thermal_zoneXX: failed to read out thermal zone (-19)

But reading from an uninitialized power supply should not be
considered as a fatal error, but the thermal core expects
the -EAGAIN error to be returned in this particular case.

So convert -ENODEV as -EAGAIN to express the fact that reading
temperature from an uninitialized power supply shouldn't be
a fatal error, but should indicate to the thermal zone it should
retry later.

It notably removes such messages on Qualcomm platforms using the
qcom_battmgr driver spawning warnings until the aDSP firmware
gets up and the battery manager reports valid data.

Link: https://lore.kernel.org/all/2ed4c630-204a-4f80-a37f-f2ca838eb455@linaro.org/


Fixes: 5bc28b93 ("power_supply: power_supply_read_temp only if use_cnt > 0")
Fixes: 3be330bf ("power_supply: Register battery as a thermal zone")
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>