Fix Switch Access settings page

The pref name referenced in the settings page did not match the setting
created in ash/pref_names.cc.

Bug: None
Change-Id: I6a83ee7aa7d454276d9fd71e0a721afb86aa717e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1642961Reviewed-by: Dan Beam <dbeam@chromium.org>
Commit-Queue: Anastasia Helfinstein <anastasi@google.com>
Cr-Commit-Position: refs/heads/master@{#665997}

chrome/browser/resources/settings/a11y_page/switch_access_subpage.html

@@ -22,7 +22,7 @@
           $i18n{assignSelectSwitchLabel}
         </div>
         <settings-dropdown-menu label="$i18n{assignSelectSwitchLabel}"
-            pref="{{prefs.switch_access.select.dropdown}}"
+            pref="{{prefs.switch_access.select.setting}}"
             menu-options="[[switchAssignOptions_]]"
             on-settings-control-change="onSelectAssigned_">
         </settings-dropdown-menu>
@@ -32,7 +32,7 @@
           $i18n{assignNextSwitchLabel}
         </div>
         <settings-dropdown-menu label="$i18n{assignNextSwitchLabel}"
-            pref="{{prefs.switch_access.next.dropdown}}"
+            pref="{{prefs.switch_access.next.setting}}"
             menu-options="[[switchAssignOptions_]]"
             on-settings-control-change="onNextAssigned_">
         </settings-dropdown-menu>
@@ -42,7 +42,7 @@
           $i18n{assignPreviousSwitchLabel}
         </div>
         <settings-dropdown-menu label="$i18n{assignPreviousSwitchLabel}"
-            pref="{{prefs.switch_access.previous.dropdown}}"
+            pref="{{prefs.switch_access.previous.setting}}"
             menu-options="[[switchAssignOptions_]]"
             on-settings-control-change="onPreviousAssigned_">
         </settings-dropdown-menu>