MAINTAINERS: Move Hartmut Knaack to Credits

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: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Andy 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: Jonathan Cameron <Jonathan.Cameron@huawei.com>

CREDITS

@@ -1942,6 +1942,10 @@ S: Post Office Box 611311
 S: San Jose, California 95161-1311
 S: USA
 
+N: Hartmut Knaack
+E: knaack.h@gmx.de
+D: IIO subsystem and drivers
+
 N: Thorsten Knabe
 E: Thorsten Knabe <tek@rbg.informatik.tu-darmstadt.de>
 E: Thorsten Knabe <tek01@hrzpub.tu-darmstadt.de>

MAINTAINERS

@@ -8451,7 +8451,6 @@ F:	drivers/iio/multiplexer/iio-mux.c
 
 IIO SUBSYSTEM AND DRIVERS
 M:	Jonathan Cameron <jic23@kernel.org>
-R:	Hartmut Knaack <knaack.h@gmx.de>
 R:	Lars-Peter Clausen <lars@metafoo.de>
 R:	Peter Meerwald-Stadler <pmeerw@pmeerw.net>
 L:	linux-iio@vger.kernel.org