[ios] Properly sets ContentSuggestionsViewController.contentSuggestionsEnabled.

This BOOL property was being intialized from the result of
PrefService::FindPreference(), which is a pointer to the pref object
rather than the value of the pref itself. This CL switches to using the
|contentSuggestionsEnabled| local var.

BUG=1142431

Change-Id: If6c13562b0bf46e12952a1a6685c48b9021462e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2497154
Commit-Queue: Sergio Collazos <sczs@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841841}

ios/chrome/browser/ui/content_suggestions/content_suggestions_coordinator.mm

@@ -298,7 +298,7 @@
       changeDiscoverFeedHeaderVisibility:[self.contentSuggestionsVisible
                                                  value]];
   self.suggestionsViewController.contentSuggestionsEnabled =
-      prefs->FindPreference(prefs::kArticlesForYouEnabled);
+      contentSuggestionsEnabled;
   self.suggestionsViewController.handler = self;
   self.contentSuggestionsMediator.consumer = self.suggestionsViewController;