dt-bindings: eeprom: at24: Fix list of page sizes for writing

"258" is an odd power-of-two ;-)
Obviously this is a typo, and the intended value is "256".

Fixes: 7f3bf420 ("dt-bindings: at24: convert the binding document to yaml")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Rob Herring <robh@kernel.org>