iio: frequency: ad9832: Remove unused parameter from data documentation

iio: frequency: ad9832: Remove unused parameter from data documentation

This is a leftover from the patch: commit 566564e80b0e ("staging: iio:
ad9832: use clock framework for clock reference").

The AD9832 driver uses the Common Clock Framework (CCF) to obtain the
master clock (MCLK) frequency rather than relying on a frequency value
passed from platform data.

Signed-off-by: Gabriel Shahrouzi <gshahrouzi@gmail.com>
Link: https://patch.msgid.link/20250417173333.607844-1-gshahrouzi@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>