dt-bindings: timer: Use non-empty ranges in example

On many arm64 qcom device trees, running `make dtbs_check` yells:

  timer@17c20000: #size-cells:0:0: 1 was expected

It appears that someone was trying to assert the fact that sub-nodes
describing frames would never have a size that's more than 32-bits
big.  That does indeed appear to be true for all cases I could find.

Currently many arm64 qcom device tree files have a #address-cells and
about in commit bede7d2d ("arm64: dts: qcom: sdm845: Increase
address and size cells for soc").  That means the only way we can
shrink them down is to use a non-empty ranges.

Since forever it has said in "writing-bindings.txt" to "DO use
non-empty 'ranges' to limit the size of child buses/devices".  I guess
we should start listening to it.

I believe (but am not certain) that this also means that we should use
"ranges" to simplify the "reg" of our sub devices by specifying an
offset.  Let's update the example in the bindings to make this
obvious.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Rob Herring <robh@kernel.org>