Fix mac build breakage.

Change-Id: Iea3d587d6975200c3680af2cc2ba53965ad249b3
diff --git a/bcinfo/MetadataExtractor.cpp b/bcinfo/MetadataExtractor.cpp
index 2537fdd..3be7e35 100644
--- a/bcinfo/MetadataExtractor.cpp
+++ b/bcinfo/MetadataExtractor.cpp
@@ -362,7 +362,7 @@
     }
   } else {
     if (mExportForEachSignatureCount != 1) {
-      ALOGE("mExportForEachSignatureCount = %u, but should be 1",
+      ALOGE("mExportForEachSignatureCount = %zu, but should be 1",
             mExportForEachSignatureCount);
     }
     char *RootName = new char[5];