[SCSI] lpfc: fix potential NULL pointer dereference in lpfc_sli4_rq_put()

The dereference to 'put_index' should be moved below the NULL test.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: James Smart <james.smart@emulex.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>