MAINTAINERS: Move Sangbeom Kim to credits

MAINTAINERS: Move Sangbeom Kim to credits

Sangbeom Kim upstreamed the Samsung SoC Sound and PMIC (MFD, regulator,
RTC) drivers.  However his contributions and LKML activity ends in 2014:
https://lore.kernel.org/lkml/?q=f%3A%22Sangbeom+Kim%22

Move Sangbeom Kim to the CREDITS file.  Thank you for the effort you put
in to the upstream Samsung support.

Link: https://lore.kernel.org/r/20201016061848.6258-2-krzk@kernel.org
Cc: Sangbeom Kim <sbkim73@samsung.com>
Cc: Sylwester Nawrocki <s.nawrocki@samsung.com>
Cc: Mark Brown <broonie@kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>