tipc: Minor optimizations to name table translation code

Optimizes TIPC's name table translation code to avoid unnecessary
manipulation of the node address field of the resulting port id when
name translation fails.  This change is possible because a valid port
id cannot have a reference field of zero, so examining the reference
only is sufficient to determine if the translation was successful.

Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>