MAINTAINERS: fix location of DT npcm files

The specified locations are not right. Fix the wildcard logic
to point to the correct directories.

Without that, get-maintainer won't get things right:

	$ ./scripts/get_maintainer.pl --no-git-fallback --no-r --no-n --no-l -f Documentation/devicetree/bindings/arm/cpu-enable-method/nuvoton,npcm750-smp
	robh+dt@kernel.org (maintainer:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS)
	mark.rutland@arm.com (maintainer:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS)

After the patch, it will properly point to NPCM arch maintainers:
	$ ./scripts/get_maintainer.pl --no-git-fallback --no-r --no-n --no-l -f Documentation/devicetree/bindings/arm/cpu-enable-method/nuvoton,npcm750-smp
	avifishman70@gmail.com (supporter:ARM/NUVOTON NPCM ARCHITECTURE)
	tmaimon77@gmail.com (supporter:ARM/NUVOTON NPCM ARCHITECTURE)
	robh+dt@kernel.org (maintainer:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS)
	mark.rutland@arm.com (maintainer:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS)

Cc: Avi Fishman <avifishman70@gmail.com>
Cc: Tomer Maimon <tmaimon77@gmail.com>
Cc: Patrick Venture <venture@google.com>
Cc: Nancy Yuen <yuenn@google.com>
Cc: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Jonathan Corbet <corbet@lwn.net>