aosp-merge.sh: use fetch --tags

Change-Id: I82a21d8f89911dd4dd3fb6787c6607374c653ea6
diff --git a/utils/aosp-merge.sh b/utils/aosp-merge.sh
index e08946b..dfd197d 100755
--- a/utils/aosp-merge.sh
+++ b/utils/aosp-merge.sh
@@ -45,7 +45,7 @@
         git remote add aosp https://android.googlesource.com/platform/$path > /dev/null
     fi
 
-    git fetch aosp
+    git fetch --tags aosp
 
     #echo "====================================================================="
     #echo " Merging {$ref}"