MAINTAINERS: Update for the current location of the bcm2835 tree.

I've been maintaining the bcm2835 branches here for a year or so.

Signed-off-by: Eric Anholt <eric@anholt.net>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>