MAINTAINERS: of: Add Saravana Kannan

Adding myself as a second maintainer for Open Firmware and Device Tree
to help Rob out with reviews and other maintainer work.

Cc: devicetree@vger.kernel.org
Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20240210231513.111117-1-saravanak@google.com


Signed-off-by: Rob Herring <robh@kernel.org>