agent/device: Fix path matching for PCI devices

For the case of virtio-blk PCI devices, when matching uevents we create
a pci_p temporary.  However, we build it incorrectly: the dev_addr values
we use for PCI devices are a relative sysfs paths from the PCI root to the
device in question *including an initial /*.  But when we construct pci_p
we add an extra /, meaning the resulting path will *not* match properly.

AFAICT the only reason we got away with this is because in practice the
virtio-blk devices where discovered by the kernel before we looked for them
meaning the loosed matching in get_device_name() was used, rather than the
pci_p logic in handle_block_add_event().

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

src/agent/src/uevent.rs

@@ -82,7 +82,7 @@ impl Uevent {
         let empties: Vec<_> = w
             .iter_mut()
             .filter(|(dev_addr, _)| {
-                let pci_p = format!("{}/{}", pci_root_bus_path, *dev_addr);
+                let pci_p = format!("{}{}", pci_root_bus_path, *dev_addr);
 
                 // blk block device
                 devpath.starts_with(pci_p.as_str()) ||