add wrapper for FFI input.open()

frontend/device/input.lua

@@ -128,6 +128,16 @@ function Input:init()
     self.event_map[10021] = "NotCharging"
 end
 
+--[[
+wrapper for FFI input open
+
+Note that we adhere to the "." syntax here for compatibility.
+TODO: clean up separation FFI/this
+--]]
+function Input.open(device)
+    input.open(device)
+end
+
 --[[
 Different device models can implement their own hooks
 and register them.