pci: Fix probe of BAR

The first BAR is not present does not mean the entire BAR are not
present. Some implementation of AHCI controller only has BAR6 present
with BAR1 to BAR5 empty.

Keep probing if a BAR is not present.

Signed-off-by: Asias He <asias@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>

drivers/pci-device.cc

@@ -39,7 +39,9 @@ namespace pci {
             u32 bar_v = pci_readl(pos);
 
             if (bar_v == 0) {
-                break;
+                pos += 4;
+                idx++;
+                continue;
             }
 
             bar * pbar = new bar(this, pos);