i2c: mpc: Use of_property_read_u32 instead of of_get_property

"of_property_read_u32()" is preferred to "of_get_property()" for
retrieving u32 from the device tree. Replace it.

Suggested-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Tested-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: Wolfram Sang <wsa@kernel.org>