MAINTAINERS: add I2C dt bindings also to I2C realm

So get_maintainer.pl will add us when something gets updated there.
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

MAINTAINERS

@@ -4561,6 +4561,7 @@ W:	https://i2c.wiki.kernel.org/
 Q:	https://patchwork.ozlabs.org/project/linux-i2c/list/
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux.git
 S:	Maintained
+F:	Documentation/devicetree/bindings/i2c/
 F:	Documentation/i2c/
 F:	drivers/i2c/
 F:	include/linux/i2c.h