MAINTAINERS: Update Calxeda Highbank maintainership

Rob sees little point in maintaining the Calxeda architecture (early ARM
32-bit server) anymore.
Since I have a machine sitting under my desk, change the maintainership
to not lose support for that platform.

Link: https://lore.kernel.org/r/20200228135106.220620-6-andre.przywara@arm.comSigned-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

MAINTAINERS

@@ -1605,7 +1605,7 @@ F:	Documentation/devicetree/bindings/clock/bitmain,bm1880-clk.yaml
 F:	Documentation/devicetree/bindings/pinctrl/bitmain,bm1880-pinctrl.txt
 
 ARM/CALXEDA HIGHBANK ARCHITECTURE
-M:	Rob Herring <robh@kernel.org>
+M:	Andre Przywara <andre.przywara@arm.com>
 L:	linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
 S:	Maintained
 F:	arch/arm/mach-highbank/