Get "num" as unsigned in ctf

Get "num" as unsigned in ctf

I see the following fail due to the warning,

-trace-frame-collected^M
[warning] Extracting signed value from an unsigned int (num)^M
....
FAIL: gdb.trace/mi-trace-frame-collected.exp: ctf: -trace-frame-collected

In ctf metadata, "num" in "tsv" is defined as unint32_t,

  ctf_save_write_metadata (&writer->tcs,
			   "event {\n\tname = \"tsv\";\n\tid = %u;\n"
			   "\tfields := struct { \n"
			   "\t\tuint64_t val;\n"
			   "\t\tuint32_t num;\n"
			   "\t};\n"
			   "};\n", CTF_EVENT_ID_TSV);

so we should read it as unsigned.  The patch below fixes the fail by
changing to bt_ctf_get_uint64.

gdb:

2016-07-22  Yao Qi  <yao.qi@linaro.org>

	* ctf.c (ctf_traceframe_info): Call bt_ctf_get_uint64 rather than
	bt_ctf_get_int64.