rpi: Make Matthias maintainer

Matthias Brugger agreed to take over maintainership from me for the
Raspberry Pi tree. Add him to the MAINTAINERS file instead.

Signed-off-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 29449ff..23c1a49 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -114,7 +114,7 @@
 N:	meson
 
 ARM BROADCOM BCM283X
-M:	Alexander Graf <agraf@suse.de>
+M:	Matthias Brugger <mbrugger@suse.com>
 S:	Maintained
 F:	arch/arm/mach-bcm283x/
 F:	drivers/gpio/bcm2835_gpio.c