dt-bindings: vendor-prefixes: document lineartechnology

Document lineartechnology vendor prefix, already used in SPI dev.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230120075618.153664-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Rob Herring <robh@kernel.org>