SUNRPC: fix _xprt_switch_find_current_entry logic

Fix the logic for picking current transport entry.

Fixes: 95d0d30c

 ("SUNRPC create an iterator to list only OFFLINE xprts")
Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>