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/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());