Update the MAINTAINERS entry and all other references accordingly.

Based on an original patch by Wolfram Sang.
Signed-off-by: NJean Delvare <khali@linux-fr.org>
Acked-by: NPeter Korsgaard <peter.korsgaard@barco.com>

[wsa: fixed merge conflict due to rework in i2c_add_mux_adapter()]
Signed-off-by: NWolfram Sang <w.sang@pengutronix.de>