MB: Fix typo in device mixin.

webrtc/build/mb_config.pyl

 # Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 # FOR DETAILS ON THIS FILE SEE THE MAIN COPY IN //tools/mb/mb_config.pyl.
 # This is configuration for standalone WebRTC bots. It is used to keep the bot
@@ skipping 37 matching lines @@
 
     'debug': {
       'gn_args': 'is_debug=true',
     },
 
     'debug_bot': {
       'mixins': ['debug', 'shared', 'goma'],
     },
 
     'device': {
-      'gn': 'ios_enable_code_signing=false',
+      'gn_args': 'ios_enable_code_signing=false',
       'gyp_defines': 'chromium_ios_signing=0',
     },
 
     'gn': {'type': 'gn'},
 
     'goma': {
       # The MB code will properly escape goma_dir if necessary in the GYP
       # code path; the GN code path needs no escaping.
       'gn_args': 'use_goma=true goma_dir="$(goma_dir)"',
       'gyp_defines': 'use_goma=1 gomadir=$(goma_dir)',
@@ skipping 59 matching lines @@
       'ios64_gn_rel': 'ios_gn_release_bot_arm64_device',
     },
   },
 
   # These lists are assumed to exist so we need them in order to be able to run
   # the mb.py script in PRESUBMIT.py to verify our config is sane.
   'common_dev_configs': [],
   'private_configs': [],
   'unsupported_configs': [],
 }