MAINTAINERS: update ti,sci.yaml reference

MAINTAINERS: update ti,sci.yaml reference

Changeset 5a9652f6994e ("dt-bindings: arm: keystone: Convert ti,sci to json schema")
renamed: Documentation/devicetree/bindings/arm/keystone/ti,sci.txt
to: Documentation/devicetree/bindings/arm/keystone/ti,sci.yaml.

Update its cross-reference accordingly.

Fixes: 5a9652f6994e ("dt-bindings: arm: keystone: Convert ti,sci to json schema")
Reviewed-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/6c9959f9d744b27908ff21a8414dcc772a45354f.1634630486.git.mchehab+huawei@kernel.org