IB/hfi1: Fix potential panic with sdma drained mechanism

The guard is backwards, potentially causing the SDMA client
to panic if a wait structure was not specified.

psm and verbs are not exposed to the issue, but fix the
code just to be correct.

Fixes: a545f530 ("staging/rdma/hfi: fix CQ completion order issue")
Reviewed-by: NDennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: NMike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: NDoug Ledford <dledford@redhat.com>

drivers/staging/rdma/hfi1/sdma.c

@@ -376,7 +376,7 @@ static inline void complete_tx(struct sdma_engine *sde,
 	sdma_txclean(sde->dd, tx);
 	if (complete)
 		(*complete)(tx, res);
-	if (iowait_sdma_dec(wait) && wait)
+	if (wait && iowait_sdma_dec(wait))
 		iowait_drain_wakeup(wait);
 }