servod: Fix init function to properly init ftdi dummy spots.

BUG=chromium:629550
TEST=Can init servod with a servo v2.

Change-Id: Ie572729cfc801d157471f353b92e983f016b7821
Reviewed-on: https://chromium-review.googlesource.com/361575
Commit-Ready: Kevin Cheng <kevcheng@chromium.org>
Tested-by: Kevin Cheng <kevcheng@chromium.org>
Tested-by: Todd Broch <tbroch@chromium.org>
Reviewed-by: Todd Broch <tbroch@chromium.org>
diff --git a/servo/servo_server.py b/servo/servo_server.py
index a3d5b77..7cb9e95 100755
--- a/servo/servo_server.py
+++ b/servo/servo_server.py
@@ -181,6 +181,17 @@
     for interface in self._interface_list:
       del(interface)
 
+  def _init_ftdi_dummy(self, interface):
+    """Dummy interface for ftdi devices.
+
+    This is a dummy function specifically for ftdi devices to not initialize
+    anything but to help pad the interface list.
+
+    Returns:
+      None.
+    """
+    return None
+
   def _init_ftdi_gpio(self, interface):
     """Initialize gpio driver interface and open for use.