IB/hfi1: Initialize bth1 in 16B rc ack builder

It is possible the bth1 variable could be used uninitialized so going
ahead and giving it a default value.

Otherwise we leak stack memory to the network.

Fixes: 5b6cabb0db77 ("IB/hfi1: Add 16B RC/UC support")
Reviewed-by: Don Hiatt <don.hiatt@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/hfi1/rc.c

@@ -814,7 +814,7 @@ static inline void hfi1_make_rc_ack_16B(struct rvt_qp *qp,
 	struct hfi1_pportdata *ppd = ppd_from_ibp(ibp);
 	struct hfi1_16b_header *hdr = &opa_hdr->opah;
 	struct ib_other_headers *ohdr;
-	u32 bth0, bth1;
+	u32 bth0, bth1 = 0;
 	u16 len, pkey;
 	u8 becn = !!is_fecn;
 	u8 l4 = OPA_16B_L4_IB_LOCAL;