Split RelativePatcher::ReserveSpace() into two.

Instead of passing nullptr and MethodReference(nullptr, 0u)
to ReserveSpace() at the end, call a newly created function
ReserveSpaceEnd().

Change-Id: I38815fe9464b4e1a919878b6e8577614f1058d00
diff --git a/compiler/linker/relative_patcher_test.h b/compiler/linker/relative_patcher_test.h
index dede42e..08167b3 100644
--- a/compiler/linker/relative_patcher_test.h
+++ b/compiler/linker/relative_patcher_test.h
@@ -98,7 +98,7 @@
       method_offset_map_.map.Put(compiled_method_refs_[idx], quick_code_offset);
       ++idx;
     }
-    offset = patcher_->ReserveSpace(offset, nullptr, MethodReference(nullptr, 0u));
+    offset = patcher_->ReserveSpaceEnd(offset);
     uint32_t output_size = offset;
     output_.reserve(output_size);