max31856 IIO driver introduced a new attribute
"in_temp_filter_notch_center_frequency".
This patch adds it to the list of documented ABI for sysfs-bus-iio
Cc: Hartmut Knaack <knaack.h@gmx.de> Cc: Lars-Peter Clausen <lars@metafoo.de> Cc: Peter Meerwald-Stadler <pmeerw@pmeerw.net> Cc: Colin Ian King <colin.king@canonical.com> Cc: Patrick Havelange <patrick.havelange@essensium.com> Cc: Matt Weber <matthew.weber@rockwellcollins.com> Cc: Matt Ranostay <matt.ranostay@konsulko.com> Cc: Chuhong Yuan <hslester96@gmail.com> Cc: Daniel Gomez <dagmcr@gmail.com> Cc: linux-iio@vger.kernel.org Signed-off-by: Andrea Merello <andrea.merello@gmail.com> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>