[iOS] Use weak self

Change-Id: I06b3adf9661acce35c6aa27ae45c68426a762ca3
Reviewed-on: https://chromium-review.googlesource.com/c/1495530Reviewed-by: David Jean <djean@chromium.org>
Commit-Queue: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636780}

ios/chrome/browser/ui/autofill/manual_fill/password_mediator.mm

@@ -220,7 +220,7 @@ BOOL AreCredentialsAtIndexesConnected(
                  action:^{
                    base::RecordAction(base::UserMetricsAction(
                        "ManualFallback_Password_OpenSuggestPassword"));
-                   [self generateAndOfferPassword];
+                   [weakSelf generateAndOfferPassword];
                  }];
       generatePasswordItem.accessibilityIdentifier =
           manual_fill::SuggestPasswordAccessibilityIdentifier;