of/numa: fix a memory@ node can only contains one memory block

For a normal memory@ devicetree node, its reg property can contains more
memory blocks.

Because we don't known how many memory blocks maybe contained, so we try
from index=0, increase 1 until error returned(the end).

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>