perf test: Print if shell directory isn't present

If the shell test directory isn't present the exit code will be 255 but
with no error messages printed. Add an error message.
Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20200313005602.45236-1-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/builtin-test.c

@@ -543,8 +543,11 @@ static int run_shell_tests(int argc, const char *argv[], int i, int width)
 		return -1;
 
 	dir = opendir(st.dir);
-	if (!dir)
+	if (!dir) {
+		pr_err("failed to open shell test directory: %s\n",
+			st.dir);
 		return -1;
+	}
 
 	for_each_shell_test(dir, st.dir, ent) {
 		int curr = i++;