powerpc: dts: Fix some I2C unit addresses

The unit-address for the Maxim MAX1237 ADCs on XPedite5200 boards don't
match the value in the "reg" property and cause a DTC warning.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211220134036.683309-1-thierry.reding@gmail.com