w1: Simplify the atribute show

There is no necessary to define variable assignment, return directly.

Signed-off-by: zuoqilin <zuoqilin@yulong.com>
Link: https://lore.kernel.org/r/20210618092418.1424-1-zuoqilin1@163.com


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>