dm: ofnode: query correct property in livetree ofnode_get_addr_size

The livetree codepath of ofnode_get_addr_size always used the "reg"
property for of_get_property. Use the property parameter of the function
call instead and check the return value if the property exists.
Otherwise return FDT_ADDR_T_NONE.

This was discoverd while using SPI NOR with livetree.
spi_flash_decode_fdt checks for memory-map and will not fail with
livetree even if the property does not exist.

Signed-off-by: Klaus Goger <klaus.goger@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>