Mask off the bar's value after the probe test write before testing

Mask off the bar's value after the probe test write before testing
against 0 in pci_alloc_map, just like we do in pci_add_map.  Also,
make sure that we restore the value to the BAR that was there before
if the bar is 0.  Chances are that it was 0 before the write too and
that the restoration is a nop, but better safe than sorry.

Notice by: dwhite