dt-binding: memory: pl353-smc: Document the range property

The ranges property is missing in the description while actually used in
the example. This property is actually needed, so mention it.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210610082040.2075611-3-miquel.raynal@bootlin.com


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>