fnic: Using rport->dd_data to check rport online instead of rport_lookup.

When issuing I/O we check if rport is online through libfc
rport_lookup() function which needs to be protected by mutex lock that
cannot acquired in I/O context. The change is to use midlayer remote
port s dd_data which is preserved until its devloss timeout and no
protection is required.  The the scsi_cmnd error code is expected to be
in the left 16 bits of the result field. Changed to correct this.  Fnic
driver version changed from 1.6.0.20 to 1.6.0.21

Signed-off-by: Satish Kharat <satishkh@cisco.com>
Signed-off-by: Sesidhar Baddela <sebaddel@cisco.com>
Reviewed-by: Ewan Milne <emilne@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>