According to the PCI Local Specification rev. 3.0 in case of a 64-bit
BAR both the low and the high parts of the register should be set to
~0 before attempting to read back the size.
So far I have found no single device that has problems with the
previous approach, but I think it's better to stay on the safe size.
This commit should not introduce any functional change.
Sponsored by: Citrix Systems R&D