devicetree: Relax initrd address assert

It doesn't matter if the initrd addresses are 64-bit pointers, even
when running on 32-bit arm, as long as the actual addresses fit in
32-bits. Relax the assert to check that condition instead.

Fixes: c6f24b86 ("lib/devicetree: Support 64 bit addresses for the initrd")
Signed-off-by: Andrew Jones <drjones@redhat.com>