[SCSI] libfc: simplify fc_lport_rport_callback

The lport rport callback can only be called for the dNS rport,
since its the only rport who's ops point to that function.

Remove unnecessary checking and debug messages.
Put the locking outside the switch statement as a simplification.

Signed-off-by: Joe Eykholt <jeykholt@cisco.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>