tracing: Fix return value of ftrace_raw_output_prep()

If the trace_seq of ftrace_raw_output_prep() is full this function
returns TRACE_TYPE_PARTIAL_LINE, otherwise it returns zero.

The problem is that TRACE_TYPE_PARTIAL_LINE happens to be zero!

The thing is, the caller of ftrace_raw_output_prep() expects a
success to be zero. Change that to expect it to be
TRACE_TYPE_HANDLED.

Link: http://lkml.kernel.org/r/20141114112522.GA2988@dhcp128.suse.cz

Reminded-by: Petr Mladek <pmladek@suse.cz>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

include/trace/ftrace.h

@@ -277,7 +277,7 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags,	\
 	field = (typeof(field))iter->ent;				\
 									\
 	ret = ftrace_raw_output_prep(iter, trace_event);		\
-	if (ret)							\
+	if (ret != TRACE_TYPE_HANDLED)					\
 		return ret;						\
 									\
 	trace_seq_printf(s, print);					\

kernel/trace/trace_output.c

@@ -196,10 +196,7 @@ int ftrace_raw_output_prep(struct trace_iterator *iter,
 	trace_seq_init(p);
 	trace_seq_printf(s, "%s: ", ftrace_event_name(event));
 
-	if (trace_seq_has_overflowed(s))
-		return TRACE_TYPE_PARTIAL_LINE;
-
-	return 0;
+	return trace_handle_return(s);
 }
 EXPORT_SYMBOL(ftrace_raw_output_prep);