dt-bindings: display: ssd132x: Remove '-' before compatible enum

This is a leftover from when the binding schema had the compatible string
property enum as a 'oneOf' child and the '-' was not removed when 'oneOf'
got dropped during the binding review process.

Reported-by: Rob Herring <robh@kernel.org>
Closes: https://lore.kernel.org/dri-devel/CAL_Jsq+h8DcnpKqhokQOODCc8+Qi3M0PrxRFKz_Y4v37yMJvvA@mail.gmail.com/
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20231020223029.1667190-1-javierm@redhat.com