ceph: fix dentry reference leak in ceph_encode_fh()

dput() was not called in the error path.

Signed-off-by: Cyril Roelandt <tipecaml@gmail.com>
Cc: Sage Weil <sage@inktank.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>