MAINTAINERS: Ben Dooks is inactive regarding I2C

Ben has done valuable work for the I2C subsystem, yet he has been
inactive for ~15 months. Let MAINTAINERS reflect that. He will be
most welcome if he wants to participate again.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: Ben Dooks <ben-linux@fluff.org>