scsi: lpfc: remove an unnecessary NULL check

Smatch complains about this code:

    drivers/scsi/lpfc/lpfc_scsi.c:1053 lpfc_get_scsi_buf_s4()
    warn: variable dereferenced before check 'lpfc_cmd' (see line 1039)

Fortunately the NULL check isn't required so I have removed it.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>