MAINTAINERS: update brcm,bcm-v3d.yaml reference

Changeset cb18a797 ("dt-bindings: gpu: Convert v3d to json-schema")
renamed: Documentation/devicetree/bindings/gpu/brcm,bcm-v3d.txt
to: Documentation/devicetree/bindings/gpu/brcm,bcm-v3d.yaml.

Update its cross-reference accordingly.

Fixes: cb18a797 ("dt-bindings: gpu: Convert v3d to json-schema")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

MAINTAINERS

@@ -6054,7 +6054,7 @@ DRM DRIVERS FOR V3D
 M:	Eric Anholt <eric@anholt.net>
 S:	Supported
 T:	git git://anongit.freedesktop.org/drm/drm-misc
-F:	Documentation/devicetree/bindings/gpu/brcm,bcm-v3d.txt
+F:	Documentation/devicetree/bindings/gpu/brcm,bcm-v3d.yaml
 F:	drivers/gpu/drm/v3d/
 F:	include/uapi/drm/v3d_drm.h