tracing/ftrace: adapt mmiotrace to the new type of print_line, fix

Correct the value's type of trace_empty function

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index b542f88..c163406 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1750,7 +1750,7 @@
 		}
 	}
 
-	return TRACE_TYPE_HANDLED;
+	return 1;
 }
 
 static enum print_line_t print_trace_line(struct trace_iterator *iter)