ARM: dts: imx6: RDU2: reduce i2c drive-strength

The current 25 Ohm drive-strength is much too strong, resulting in
significant overshoot of the signal. Reduce the drive-strength to
75 Ohm to get rid of those issues.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>