MAINTAINERS: add devicetree bindings to Input Drivers section

To avoid changes to input bindings not reaching linux-input reviewers
add an appropriate file pattern to the MAINTAINERS entry.
Reported-by: Heiko Stübner <heiko@sntech.de>
Signed-off-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

MAINTAINERS

@@ -5476,6 +5476,7 @@ F:	drivers/input/
 F:	include/linux/input.h
 F:	include/uapi/linux/input.h
 F:	include/linux/input/
+F:	Documentation/devicetree/bindings/input/
 
 INPUT MULTITOUCH (MT) PROTOCOL
 M:	Henrik Rydberg <rydberg@bitmath.org>