tools/perf/tests: Fix compilation error with strncpy in tests/tool_pmu

perf fails to compile on systems with GCC version11
as below:

In file included from /usr/include/string.h:519,
                 from /home/athir/perf-tools-next/tools/include/linux/bitmap.h:5,
                 from /home/athir/perf-tools-next/tools/perf/util/pmu.h:5,
                 from /home/athir/perf-tools-next/tools/perf/util/evsel.h:14,
                 from /home/athir/perf-tools-next/tools/perf/util/evlist.h:14,
                 from tests/tool_pmu.c:3:
In function ‘strncpy’,
    inlined from ‘do_test’ at tests/tool_pmu.c:25:3:
/usr/include/bits/string_fortified.h:95:10: error: ‘__builtin_strncpy’ specified bound 128 equals destination size [-Werror=stringop-truncation]
   95 |   return __builtin___strncpy_chk (__dest, __src, __len,
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   96 |                                   __glibc_objsize (__dest));
      |                                   ~~~~~~~~~~~~~~~~~~~~~~~~~

The compile error is from strncpy refernce in do_test:
	strncpy(str, tool_pmu__event_to_str(ev), sizeof(str));

This behaviour is not observed with GCC version 8, but observed
with GCC version 11 . This is message from gcc for detecting
truncation while using strncpu. Use snprintf instead of strncpy
here to be safe.

Signed-off-by: Athira Rajeev <[email protected]>
Signed-off-by: Namhyung Kim <[email protected]>

tools/perf/tests/tool_pmu.c

@@ -22,7 +22,7 @@ static int do_test(enum tool_pmu_event ev, bool with_pmu)
 	if (with_pmu)
 		snprintf(str, sizeof(str), "tool/%s/", tool_pmu__event_to_str(ev));
 	else
-		strncpy(str, tool_pmu__event_to_str(ev), sizeof(str));
+		snprintf(str, sizeof(str), "%s", tool_pmu__event_to_str(ev));
 
 	parse_events_error__init(&err);
 	ret = parse_events(evlist, str, &err);