dt-bindings: interrupt-controller: update brcm,l2-intc.yaml reference

Changeset 539d25b2 ("dt-bindings: interrupt-controller: Convert Broadcom STB L2 to YAML")
renamed: Documentation/devicetree/bindings/interrupt-controller/brcm,l2-intc.txt
to: Documentation/devicetree/bindings/interrupt-controller/brcm,l2-intc.yaml.

Update its cross-reference accordingly.

Fixes: 539d25b2

 ("dt-bindings: interrupt-controller: Convert Broadcom STB L2 to YAML")
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/a40c02a7aaea91ea7b6ce24b6bc574ae5bcf4cf6.1654529011.git.mchehab@kernel.org