Fix padding computation in ArenaAllocator::AllocAlign16() am: 68353fecf7

Original change: https://android-review.googlesource.com/c/platform/art/+/2202585

Change-Id: Idc74eb92a8d92fdf970b6cc9e895f921592fa5ca
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>
diff --git a/libartbase/base/arena_allocator.h b/libartbase/base/arena_allocator.h
index 12a44d5..bf7d932 100644
--- a/libartbase/base/arena_allocator.h
+++ b/libartbase/base/arena_allocator.h
@@ -289,7 +289,7 @@
       return AllocWithMemoryToolAlign16(bytes, kind);
     }
     uintptr_t padding =
-        ((reinterpret_cast<uintptr_t>(ptr_) + 15u) & 15u) - reinterpret_cast<uintptr_t>(ptr_);
+        RoundUp(reinterpret_cast<uintptr_t>(ptr_), 16) - reinterpret_cast<uintptr_t>(ptr_);
     ArenaAllocatorStats::RecordAlloc(bytes, kind);
     if (UNLIKELY(padding + bytes > static_cast<size_t>(end_ - ptr_))) {
       static_assert(kArenaAlignment >= 16, "Expecting sufficient alignment for new Arena.");