dt-bindings: i2c: aspeed: Drop stray '#interrupt-cells'

'#interrupt-cells' is not documented which causes a warning when
'unevaluatedProperties' is implemented. Unless the I2C controller is
also an interrupt controller, '#interrupt-cells' is not valid. This
doesn't appear to be the case from the driver, so just remove it from
the example.

Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>