tracing: Add a seq_buf_clear() helper and clear len and readpos in init

Add a helper function seq_buf_clear() that resets the len and readpos
fields of a seq_buf. Currently it is only used in the seq_buf_init()
but will be used later when updating the seq_file code.

Link: http://lkml.kernel.org/r/20141104160222.352309995@goodmis.org

Tested-by: Jiri Kosina <jkosina@suse.cz>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Reviewed-by: Petr Mladek <pmladek@suse.cz>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

include/linux/seq_buf.h

@@ -22,13 +22,18 @@ struct seq_buf {
 	loff_t			readpos;
 };
 
+static inline void seq_buf_clear(struct seq_buf *s)
+{
+	s->len = 0;
+	s->readpos = 0;
+}
+
 static inline void
 seq_buf_init(struct seq_buf *s, unsigned char *buf, unsigned int size)
 {
 	s->buffer = buf;
 	s->size = size;
-	s->len = 0;
-	s->readpos = 0;
+	seq_buf_clear(s);
 }
 
 /*