Camera: Fix metadata generation on OS X.

- readlink has no -f option.
- mktemp requires a template

Change-Id: I77e2fd6a664cda5edeeeb4d781ab5439d6c7c507
diff --git a/camera/docs/metadata-generate b/camera/docs/metadata-generate
index 7869763..8e5bf56 100755
--- a/camera/docs/metadata-generate
+++ b/camera/docs/metadata-generate
@@ -23,7 +23,7 @@
 #   ../src/camera_metadata_tags.h
 #
 
-thisdir=$(dirname $(readlink -f $0))
+thisdir=$(cd "$(dirname "$0")"; pwd)
 
 function relpath() {
     python -c "import os.path; print os.path.relpath('$1', '$PWD')"