selftests/powerpc: Use snprintf to construct DSCR sysfs interface paths

Currently sprintf is used, and while paths should never exceed
the size of the buffer it is theoretically possible since
dirent.d_name is 256 bytes. As a result this trips
-Wformat-overflow, and since the test is built with -Wall -Werror
the causes the build to fail. Switch to using snprintf and skip
any paths which are too long for the filename buffer.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

tools/testing/selftests/powerpc/dscr/dscr_sysfs_test.c

@@ -53,14 +53,18 @@ static int check_all_cpu_dscr_defaults(unsigned long val)
 	}
 
 	while ((dp = readdir(sysfs))) {
+		int len;
+
 		if (!(dp->d_type & DT_DIR))
 			continue;
 		if (!strcmp(dp->d_name, "cpuidle"))
 			continue;
 		if (!strstr(dp->d_name, "cpu"))
 			continue;
 
-		sprintf(file, "%s%s/dscr", CPU_PATH, dp->d_name);
+		len = snprintf(file, LEN_MAX, "%s%s/dscr", CPU_PATH, dp->d_name);
+		if (len >= LEN_MAX)
+			continue;
 		if (access(file, F_OK))
 			continue;