clippy: Address the issue 'needless-borrow'

Issue from beta verion of clippy:

Error:    --> vm-virtio/src/queue.rs:700:59
    |
700 |             if let Some(used_event) = self.get_used_event(&mem) {
    |                                                           ^^^^ help: change this to: `mem`
    |
    = note: `-D clippy::needless-borrow` implied by `-D warnings`
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow

Signed-off-by: Bo Chen <chen.bo@intel.com>

virtio-devices/src/transport/pci_device.rs

@@ -652,7 +652,7 @@ impl VirtioPciDevice {
 
         if offset < std::mem::size_of::<VirtioPciCap>() {
             let (_, right) = cap_slice.split_at_mut(offset);
-            right[..data_len].copy_from_slice(&data);
+            right[..data_len].copy_from_slice(data);
             None
         } else {
             // Safe since we know self.cap_pci_cfg_info.cap.cap.offset is 32bits long.