Also apply prefix when dumping isAllowedToUseHiddenApi

This is a follow up CL to a CL [1] that added one more state dump from
ApplicationInfo regarding whether the app is exampted from the API
restriction but forgot to take care of prefix handling.

 [1]: I01e837253d00c6ffa841a9e5c226204a3e11b827
      974290b032b4d98603925d36851422986a5d7d0e

Bug: 64382372
Test: Ran the following command to see "isAllowedToUseHiddenApi"
      is aligned with other outputs from ApplicationInfo.
         adb shell ime list -a
Change-Id: I9c77d9b557245b7f3b51631140bd564feef601ce
diff --git a/core/java/android/content/pm/ApplicationInfo.java b/core/java/android/content/pm/ApplicationInfo.java
index efa90d3..387a836 100644
--- a/core/java/android/content/pm/ApplicationInfo.java
+++ b/core/java/android/content/pm/ApplicationInfo.java
@@ -1188,7 +1188,7 @@
             if (category != CATEGORY_UNDEFINED) {
                 pw.println(prefix + "category=" + category);
             }
-            pw.println("isAllowedToUseHiddenApi=" + isAllowedToUseHiddenApi());
+            pw.println(prefix + "isAllowedToUseHiddenApi=" + isAllowedToUseHiddenApi());
         }
         super.dumpBack(pw, prefix);
     }