Use correct API version for UTF-8 checking

Use the constant for checking the API version in aapt instead of a bare
number.

Bug: 2541326
Change-Id: Ice7af7b393363a00f1832dd84753b8138d057fb4
diff --git a/tools/aapt/Resource.cpp b/tools/aapt/Resource.cpp
index a8ac2ec..cafd635 100644
--- a/tools/aapt/Resource.cpp
+++ b/tools/aapt/Resource.cpp
@@ -775,7 +775,7 @@
      * allow UTF-8 to be used.
      */
     if (!bundle->getWantUTF16()
-            && bundle->isUTF8Available()) {
+            && bundle->isMinSdkAtLeast(SDK_FROYO)) {
         xmlFlags |= XML_COMPILE_UTF8;
     }