MAINTAINERS / Documentation: Thorsten Scherer is the successor of Gavin Schenk

Due to new challenges in my life I can no longer take care of SIOX.
Thorsten takes over my SIOX tasks.

Signed-off-by: Gavin Schenk <g.schenk@eckelmann.de>
Acked-by: Thorsten Scherer <t.scherer@eckelmann.de>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>