Settings: Update icon sizes for zen auto rules.

Bug: 21474291
Change-Id: I5f2ec0e86f9390ee9c73e4a1be6bc280162b1cab
diff --git a/res/drawable/ic_add.xml b/res/drawable/ic_add.xml
index 5939c97..e4ced7d 100644
--- a/res/drawable/ic_add.xml
+++ b/res/drawable/ic_add.xml
@@ -14,8 +14,8 @@
     limitations under the License.
 -->
 <vector xmlns:android="http://schemas.android.com/apk/res/android"
-        android:width="32.0dp"
-        android:height="32.0dp"
+        android:width="24.0dp"
+        android:height="24.0dp"
         android:viewportWidth="48.0"
         android:viewportHeight="48.0">
     <path