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.

virtio-devices/src/vhost_user/fs.rs

@@ -302,7 +302,7 @@ impl Fs {
         let num_queues = NUM_QUEUE_OFFSET + req_num_queues;
 
         // Connect to the vhost-user socket.
-        let mut vhost_user_fs = connect_vhost_user(false, &path, num_queues as u64, false)?;
+        let mut vhost_user_fs = connect_vhost_user(false, path, num_queues as u64, false)?;
 
         // Filling device and vring features VMM supports.
         let avail_features = DEFAULT_VIRTIO_FEATURES;

virtio-devices/src/vsock/unix/muxer.rs

@@ -234,7 +234,7 @@ impl VsockChannel for VsockMuxer {
             // connection requests.
             if pkt.op() == uapi::VSOCK_OP_REQUEST {
                 // Oh, this is a connection request!
-                self.handle_peer_request_pkt(&pkt);
+                self.handle_peer_request_pkt(pkt);
             } else {
                 // Send back an RST, to let the drive know we weren't expecting this packet.
                 self.enq_rst(pkt.dst_port(), pkt.src_port());