dt-bindings:iio:qcom-spmi-vadc drop incorrect io-channel-ranges from example

io-channel-ranges is a property for io-channel consumers. Here
it is in an example of a provider of channels so doesn't do anything
useful.

Recent additions to dt-schema check this property is only provided
alongside io-channels which is not true here and hence an error is
reported.

Reported-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Andy Gross <agross@kernel.org>
Cc: Jishnu Prakash <jprakash@codeaurora.org>
Link: https://lore.kernel.org/r/20201115192951.1073632-2-jic23@kernel.org