scsi: ibmvscsi_tgt: Remove unneeded variable rc

Variable rc is not modified in ibmvscsis_srp_i_logout function.  So remove
unneeded variable rc.

Issue found using coccicheck tool.

Link: https://lore.kernel.org/r/20191101120407.GA9369@saurav


Signed-off-by: Saurav Girepunje <saurav.girepunje@gmail.com>
Reviewed-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>