qvm-run-vm: appease ShellCheck without comment

qubes-rpc/qvm-run-vm

@@ -44,8 +44,7 @@ VMNAME="$1"
 shift
 
 if [ "$VMNAME" = "--dispvm" ] ; then
-    # shellcheck disable=SC2016
-    VMNAME='$dispvm'
+    VMNAME="\$dispvm"
 elif [ "$VMNAME" = "" ] ; then
     print_usage
     exit 1