ftrace: ktime.h not included in ftrace.h

Including <linux/ktime.h> eliminates the following error:

include/linux/ftrace.h:220: error: expected specifier-qualifier-list
before 'ktime_t'
Signed-off-by: Steven Noonan <steven@uplinklabs.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/ftrace.h

@@ -3,6 +3,7 @@
 
 #include <linux/linkage.h>
 #include <linux/fs.h>
+#include <linux/ktime.h>
 #include <linux/init.h>
 #include <linux/types.h>
 #include <linux/kallsyms.h>