perf target: Fix check on buffer size

It was a mistake just replace assert to BUG_ON since its condition
should be negated. Fix it.
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ulrich Drepper <drepper@gmail.com>
Link: http://lkml.kernel.org/r/1343267410-7758-1-git-send-email-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/target.c

@@ -110,7 +110,7 @@ int perf_target__strerror(struct perf_target *target, int errnum,
 	int idx;
 	const char *msg;
 
-	BUG_ON(buflen > 0);
+	BUG_ON(buflen == 0);
 
 	if (errnum >= 0) {
 		const char *err = strerror_r(errnum, buf, buflen);