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.

Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Joel Stanley <joel@jms.id.au>
Cc: Andrew Jeffery <andrew@aj.id.au>
Cc: Rayn Chen <rayn_chen@aspeedtech.com>
Cc: linux-i2c@vger.kernel.org
Cc: openbmc@lists.ozlabs.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-aspeed@lists.ozlabs.org
Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20211206174237.2298580-1-robh@kernel.org