tracing/kprobe: Show sign of fields in trace_kprobe format files

The format files of trace_kprobe do not show the sign of the fields.
The other format files show the field signed type of the fields and
this patch makes the trace_kprobe formats consistent with the others.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
LKML-Reference: <4B273D27.5040009@cn.fujitsu.com>
Acked-by: Masami Hiramatsu <mhiramat@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>