MAINTAINERS: add DT binding docs for AT24

The driver gained DT support recently, so we should add the binding docs
in the MAINTAINERS file.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>