[IB/mthca]: Fix error CQ entry handling on mem-free HCAs

Fix handling of error CQ entries on mem-free HCAs: the doorbell count
is never valid so we shouldn't look at it.  This fixes problems exposed
by new HCA firmware.

Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/mthca/mthca_cq.c

@@ -373,8 +373,12 @@ static int handle_error_cqe(struct mthca_dev *dev, struct mthca_cq *cq,
 	 * If we're at the end of the WQE chain, or we've used up our
 	 * doorbell count, free the CQE.  Otherwise just update it for
 	 * the next poll operation.
+	 *
+	 * This does not apply to mem-free HCAs: they don't use the
+	 * doorbell count field, and so we should always free the CQE.
 	 */
-	if (!(new_wqe & cpu_to_be32(0x3f)) || (!cqe->db_cnt && dbd))
+	if (mthca_is_memfree(dev) ||
+	    !(new_wqe & cpu_to_be32(0x3f)) || (!cqe->db_cnt && dbd))
 		return 0;
 
 	cqe->db_cnt   = cpu_to_be16(be16_to_cpu(cqe->db_cnt) - dbd);