IPoIB: Correct debugging output when path record lookup fails

If path_rec_completion() is passed a non-NULL path record pointer
along with an unsuccessful status value, the tracing code incorrectly
prints the (invalid) DLID from the path record rather than the more
interesting status code.  The actual logic of the function correctly
uses the path record only if the status indicates a successful lookup.

Signed-off-by: Roland Dreier <rolandd@cisco.com>