RDMA/cxgb4: Restore the dropped uninitialized_var

In some configurations even gcc 7 cannot unravel this complexity and still
throws a warning.

Fixes: 4ab39e2f ("RDMA/cxgb4: Make c4iw_poll_cq_one() easier to analyze")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/cxgb4/cq.c

@@ -671,7 +671,7 @@ static int poll_cq(struct t4_wq *wq, struct t4_cq *cq, struct t4_cqe *cqe,
 static int __c4iw_poll_cq_one(struct c4iw_cq *chp, struct c4iw_qp *qhp,
 			      struct ib_wc *wc)
 {
-	struct t4_cqe cqe;
+	struct t4_cqe uninitialized_var(cqe);
 	struct t4_wq *wq = qhp ? &qhp->wq : NULL;
 	u32 credit = 0;
 	u8 cqe_flushed;