iio: adc: qcom-spmi-adc5: Remove unnecessary datasheet_name NULL check

datasheet_name is statically filled by a macro for every channel, and is
nor should ever be set to NULL.

Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20230502-iio-adc-propagate-fw-node-label-v3-4-6be5db6e6b5a@somainline.org


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>