scsi: libcxgbi: remove redundant check and close on csk

csk is always null on the error return path and so the non-null check
and call to cxgbi_sock_closed on csk is redundant and can be removed.

Detected by: CoverityScan CID#114329 ("Logically dead code")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Varun Prakash <varun@chelsio.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>