virtio-devices: Fix clippy warning for use of .clone()

warning: `devices` (lib) generated 1 warning (run `cargo clippy --fix --lib -p devices` to apply 1 suggestion)
warning: assigning the result of `Clone::clone()` may be inefficient
    --> virtio-devices/src/transport/pci_device.rs:1073:9
     |
1073 |         self.bar_regions = bars.clone();
     |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `clone_from()`: `self.bar_regions.clone_from(&bars)`
     |
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#assigning_clones

Signed-off-by: Rob Bradford <rbradford@rivosinc.com>

virtio-devices/src/transport/pci_device.rs

@@ -1070,7 +1070,7 @@ impl PciDevice for VirtioPciDevice {
             bars.push(bar);
         }
 
-        self.bar_regions = bars.clone();
+        self.bar_regions.clone_from(&bars);
 
         Ok(bars)
     }