MFD maintainer

We probably need someone to look after the few drivers/mfd patches coming
every now and then.  As agreed with Andrew, I'm ok to do so and my
employer is fine with me spending a few working hours on it, if needed.
Ben, Philipp, feel free to add your names there too if you wish.

Signed-off-by: Samuel Ortiz <sameo@openedhand.com>
Cc: "pHilipp Zabel" <philipp.zabel@gmail.com>
Cc: Ian Molton <spyro@f2s.com>
Cc: Ben Dooks <ben-linux@fluff.org>
Cc: Dmitry Baryshkov <dbaryshkov@gmail.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>