tracing: avoid warnings from zero-arg tracepoints

Tracepoints with no arguments can issue two warnings:

	"field" defined by not used
	"ret" is uninitialized in this function

Mark field as being OK to leave unused, and initialize ret.

[ Impact: fix false positive compiler warnings. ]
Signed-off-by: NJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
Cc: mathieu.desnoyers@polymtl.ca
LKML-Reference: <1239950139-1119-5-git-send-email-jeremy@goop.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

include/trace/ftrace.h

@@ -160,8 +160,8 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags)	\
 static int								\
 ftrace_format_##call(struct trace_seq *s)				\
 {									\
-	struct ftrace_raw_##call field;					\
-	int ret;							\
+	struct ftrace_raw_##call field __attribute__((unused));		\
+	int ret = 0;							\
 									\
 	tstruct;							\
 									\