MAINTAINERS: move Kamil Debski to credits

Kamil Debski has not been active on LKML since 2017:
https://lore.kernel.org/lkml/?q=f%3A%22Kamil+Debski%22



Move Kamil Debski to the CREDITS file.  Thank you for the effort you put
in to the upstream Linux kernel work.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Cc: Kamil Debski <kamil@wypas.org>
Cc: Andrzej Hajda <a.hajda@samsung.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Sylwester Nawrocki <s.nawrocki@samsung.com>
Link: https://lore.kernel.org/r/20201016151528.7553-1-krzk@kernel.org