libceph: fix error handling in handle_reply()

We've tried to fix the error paths in this function before, but there
is still a hidden goto in the ceph_decode_need() macro which goes to the
wrong place.  We need to release the "req" and unlock a mutex before
returning.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Sage Weil <sage@inktank.com>