arm64: dts: stratix10: fix incorrect I2C property for SCL signal

The correct dts property for the SCL falling time is
"i2c-scl-falling-time-ns".

Fixes: c8da1d15

 ("arm64: dts: stratix10: i2c clock running out of spec")
Cc: stable@vger.kernel.org
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>