Fix class cast issue in AddItemActivity am: 671ffb88ca am: 414e50b0f3 am: 14f90e1a3e

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Launcher3/+/15299573

Change-Id: Ieaab362a75aa6d11a23c1ff1886ad2677b27ccfc