s390/qdio: consider ERROR buffers for inbound-full condition

In the unlikely case that an ERROR buffer (presented by the HW)
consumed the last available slot on the input queue, increment the
corresponding statistics counter.

Signed-off-by: Julian Wiedmann <[e-mail]>
Reviewed-by: Benjamin Block <[e-mail]>
Signed-off-by: Martin Schwidefsky <[e-mail]>

drivers/s390/cio/qdio_main.c

···
 	case SLSB_P_INPUT_ERROR:
 		process_buffer_error(q, count);
 		q->first_to_check = add_buf(q->first_to_check, count);
-		atomic_sub(count, &q->nr_buf_used);
+		if (atomic_sub_return(count, &q->nr_buf_used) == 0)
+			qperf_inc(q, inbound_queue_full);
 		if (q->irq_ptr->perf_stat_enabled)
 			account_sbals_error(q, count);
 		break;