[PATCH] trace: Fix build breakage without CONFIG_PERF_EVENTS

[Mark Brown <broonie@opensource.wolfsonmicro.com>]

Today's -next fails to build for me:

  CC      kernel/trace/trace_export.o
In file included from kernel/trace/trace_export.c:197: kernel/trace/trace_entries.h:58: error: 'perf_ftrace_event_register' undeclared here (not in a function)
make[2]: *** [kernel/trace/trace_export.o] Error 1
make[1]: *** [kernel/trace] Error 2
make: *** [kernel] Error 2

because as of ced390 (ftrace, perf: Add support to use function
tracepoint in perf) perf_trace_event_register() is declared in trace.h
only if CONFIG_PERF_EVENTS is enabled but I don't have that set.

Ensure that we always have a definition of perf_trace_event_register()
by providing a definition if CONFIG_PERF_EVENTS is disabled.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
---

This one had the build test run all the way...

 kernel/trace/trace.h |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 54faec7..2aef24e 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -842,6 +842,8 @@ int perf_ftrace_event_register(struct ftrace_event_call *call,
 #else
 #define perf_ftrace_event_register NULL
 #endif /* CONFIG_FUNCTION_TRACER */
+#else
+#define perf_ftrace_event_register NULL
 #endif /* CONFIG_PERF_EVENTS */
 
 #endif /* _LINUX_KERNEL_TRACE_H */
-- 
1.7.9.1