dt-bindings: mtd: nvmem-cells: Drop range property from example

Memory mapped devices such as parallel NOR flash could make use of the
'ranges' property to translate a nvmem 'reg' cell address to a CPU
address but in practice there is no upstream user nor any declaration of
this property being valid in this case yet, leading to a warning when
constraining a bit more the schema:

	.../mtd/partitions/nvmem-cells.example.dtb: calibration@f00000:
	Unevaluated properties are not allowed ('ranges' was unexpected)

So let's drop the property from the example, knowing that someone might
actually properly define it some day.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/linux-mtd/20221114090315.848208-14-miquel.raynal@bootlin.com