arm64: tegra: Drop incorrect maxim,disable-etr on Smaug

There is no "maxim,disable-etr" property (but there is
maxim,enable-etr), neither in the bindings nor in the Linux driver:

  tegra210-smaug.dtb: regulator@1c: Unevaluated properties are not allowed ('maxim,disable-etr' was unexpected)

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Diogo Ivo <diogo.ivo@tecnico.ulisboa.pt>
Signed-off-by: Thierry Reding <treding@nvidia.com>