MAINTAINERS: update mtk-sd.yaml reference

Changeset c626695e ("dt-bindings: mmc: Convert mtk-sd to json-schema")
renamed: Documentation/devicetree/bindings/mmc/mtk-sd.txt
to: Documentation/devicetree/bindings/mmc/mtk-sd.yaml.

Update its cross-reference accordingly.

Fixes: c626695e ("dt-bindings: mmc: Convert mtk-sd to json-schema")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

MAINTAINERS

@@ -11278,7 +11278,7 @@ F:	drivers/media/platform/mtk-vpu/
 MEDIATEK MMC/SD/SDIO DRIVER
 M:	Chaotian Jing <chaotian.jing@mediatek.com>
 S:	Maintained
-F:	Documentation/devicetree/bindings/mmc/mtk-sd.txt
+F:	Documentation/devicetree/bindings/mmc/mtk-sd.yaml
 F:	drivers/mmc/host/mtk-sd.c
 
 MEDIATEK MT76 WIRELESS LAN DRIVER