MAINTAINERS: add include/dt-bindings/mips to MIPS

Maintainers of the directory Documentation/devicetree/bindings/mips
are also the maintainers of the corresponding directory
include/dt-bindings/mips.

Add the file entry for include/dt-bindings/mips to the appropriate
section in MAINTAINERS.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

MAINTAINERS

@@ -13345,6 +13345,7 @@ F:	Documentation/devicetree/bindings/mips/
 F:	Documentation/mips/
 F:	arch/mips/
 F:	drivers/platform/mips/
+F:	include/dt-bindings/mips/
 
 MIPS BOSTON DEVELOPMENT BOARD
 M:	Paul Burton <paulburton@kernel.org>