iio: common: scmi_sensors: use HZ macro from units.h

Remove duplicated definition of UHZ_PER_HZ, because it's available in
the units.h as MICROHZ_PER_HZ.

Signed-off-by: Dmitry Rokosov <ddrokosov@sberdevices.ru>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220812165243.22177-5-ddrokosov@sberdevices.ru


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