of/fdt: fix phys_addr_t related print size warnings

Fix warnings in early_init_dt_reserve_memory_arch when phys_addr_t is
32-bit and memblock is not enabled.

Signed-off-by: Rob Herring <robh@kernel.org>
Tested-by: Grant Likely <grant.likely@linaro.org>
Tested-by: Stephen Chivers <schivers@csc.com>