scsi_transport_fc: Unexport scsi_is_fc_vport()

Running the command "git grep -nHw scsi_is_fc_vport" shows that this
function is only called from inside scsi_transport_fc.c. Hence unexport
this function.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: James Smart <james.smart@avagotech.com>
Reviewed-by: Hannes Reinicke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>