tracing: Convert seq_buf fields to be like seq_file fields

In facilitating the conversion of seq_file to use seq_buf,
have the seq_buf fields match the types used by seq_file.

Link: http://lkml.kernel.org/r/20141104160222.195301024@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>