tracing: Fix undeclared ENOSYS in include/linux/tracepoint.h

The header file include/linux/tracepoint.h may be included without
include/linux/errno.h and then the compiler will fail on building for
undelcared ENOSYS. This patch fixes this problem via including <linux/errno.h>
to include/linux/tracepoint.h.
Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
LKML-Reference: <1277118549-622-1-git-send-email-wuzhangjin@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

include/linux/tracepoint.h

@@ -14,6 +14,7 @@
  * See the file COPYING for more details.
  */
 
+#include <linux/errno.h>
 #include <linux/types.h>
 #include <linux/rcupdate.h>