memblock: allow zero threshold in validate_numa_converage()

Currently memblock validate_numa_converage() returns false negative when
threshold set to zero.

Make the check if the memory size with invalid node ID is greater than
the threshold exclusive to fix that.

Link: https://lore.kernel.org/all/Z0mIDBD4KLyxyOCm@kernel.org/


Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>