iio: accel: adxl380: fix raw sample read

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>