bus: mvebu-mbus: Fix optional pcie-mem/io-aperture properties

If the property was not specified then the returned resource had a
resource_size(..) == 1, rather than 0. The PCI-E driver checks for 0 so it
blindly continues on with a corrupted resource.

The regression was introduced into v3.12 by:

  11be6547 PCI: mvebu: Adapt to the new device tree layout

Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>