Clean up Scoped-/ArenaAlocator array allocations.

Change-Id: Id718f8a4450adf1608306286fa4e6b9194022532
diff --git a/compiler/dex/quick/mir_to_lir.h b/compiler/dex/quick/mir_to_lir.h
index 9f1a497..88ca911 100644
--- a/compiler/dex/quick/mir_to_lir.h
+++ b/compiler/dex/quick/mir_to_lir.h
@@ -592,7 +592,7 @@
     // strdup(), but allocates from the arena.
     char* ArenaStrdup(const char* str) {
       size_t len = strlen(str) + 1;
-      char* res = reinterpret_cast<char*>(arena_->Alloc(len, kArenaAllocMisc));
+      char* res = arena_->AllocArray<char>(len, kArenaAllocMisc);
       if (res != NULL) {
         strncpy(res, str, len);
       }