Hartmut Knaack was an active reviewer and contributor to the IIO
subsystem and drivers.  However his last message on LKML is from
October 2015.

In thanks for Hartmut's effort, move him name to the Credits.
Suggested-by: NAndy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: NKrzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: NAndy Shevchenko <andy.shevchenko@gmail.com>
Cc: Jonathan Cameron <jic23@kernel.org>
Cc: linux-iio <linux-iio@vger.kernel.org>
Link: https://lore.kernel.org/r/20200903181926.5606-2-krzk@kernel.orgSigned-off-by: NJonathan Cameron <Jonathan.Cameron@huawei.com>