power: supply: max17040: Check iio_read_channel_processed() return code

power: supply: max17040: Check iio_read_channel_processed() return code

Since iio_read_channel_processed() may fail, return its exit code on error.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 814755c48f8b ("power: max17040: get thermal data from adc if available")
Signed-off-by: Ivan Abramov <i.abramov@mt-integration.ru>
Link: https://patch.msgid.link/20251008133648.559286-1-i.abramov@mt-integration.ru
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>