iio: hid-sensor-prox: support multi-channel SCALE calculation

iio: hid-sensor-prox: support multi-channel SCALE calculation

With the introduction of multi-channel support in commit 596ef5cf654b
("iio: hid-sensor-prox: Add support for more channels"), each channel
requires an independent SCALE calculation, but the existing code only
calculates SCALE for a single channel.

Addresses the problem by modifying the driver to perform independent
SCALE calculations for each channel.

Cc: stable@vger.kernel.org
Fixes: 596ef5cf654b ("iio: hid-sensor-prox: Add support for more channels")
Signed-off-by: Zhang Lixu <lixu.zhang@intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Link: https://patch.msgid.link/20250331055022.1149736-3-lixu.zhang@intel.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>