MAINTAINERS: iio: move Peter Meerwald-Stadler to CREDITS

Haven't had much time lately and moved on to different things.
Thanks Jonathan for the gentle introduction to Linux land.

Signed-off-by: Peter Meerwald-Stadler <pmeerw@pmeerw.net>
Reviewed-by: Matt Ranostay <matt.ranostay@konsulko.com>
Link: https://lore.kernel.org/r/20210125195654.580465-1-pmeerw@pmeerw.net


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