iio: accel: adxl380: fix raw sample read

[ Upstream commit bfa335f18d91c52fa0f8ba3e4d49afebbd9ee792 ]

The adxl380_read_chn function returns either a negative value in case an
error occurs or the actual sample.

Check only for negative values after a channel is read.

Fixes: df36de13 ("iio: accel: add ADXL380 driver")
Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Link: https://patch.msgid.link/20241101095202.20121-1-antoniu.miclaus@analog.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>