IB/mthca: Make functions that never fail return void

The function mthca_free_err_wqe() can never fail, so get rid of its
return value.  That means handle_error_cqe() doesn't have to check
what mthca_free_err_wqe() returns, which means it can't fail either
and doesn't have to return anything either.  All this results in
simpler source code and a slight object code improvement:

add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-10 (-10)
function                                     old     new   delta
mthca_free_err_wqe                            83      81      -2
mthca_poll_cq                               1758    1750      -8

Signed-off-by: Roland Dreier <rolandd@cisco.com>
diff --git a/drivers/infiniband/hw/mthca/mthca_dev.h b/drivers/infiniband/hw/mthca/mthca_dev.h
index e4810372..c98628a 100644
--- a/drivers/infiniband/hw/mthca/mthca_dev.h
+++ b/drivers/infiniband/hw/mthca/mthca_dev.h
@@ -495,8 +495,8 @@
 			  struct ib_send_wr **bad_wr);
 int mthca_arbel_post_receive(struct ib_qp *ibqp, struct ib_recv_wr *wr,
 			     struct ib_recv_wr **bad_wr);
-int mthca_free_err_wqe(struct mthca_dev *dev, struct mthca_qp *qp, int is_send,
-		       int index, int *dbd, __be32 *new_wqe);
+void mthca_free_err_wqe(struct mthca_dev *dev, struct mthca_qp *qp, int is_send,
+			int index, int *dbd, __be32 *new_wqe);
 int mthca_alloc_qp(struct mthca_dev *dev,
 		   struct mthca_pd *pd,
 		   struct mthca_cq *send_cq,