testcases: Constify char *msg variable.

The parse_opts() now returns const char * instead of char * this commit
fixes all warnings caused by the change.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
diff --git a/testcases/kernel/syscalls/flock/flock03.c b/testcases/kernel/syscalls/flock/flock03.c
index a7a1cd9..b2734b5 100644
--- a/testcases/kernel/syscalls/flock/flock03.c
+++ b/testcases/kernel/syscalls/flock/flock03.c
@@ -62,7 +62,7 @@
 int main(int argc, char **argv)
 {
 	int lc;
-	char *msg;
+	const char *msg;
 	pid_t pid;
 	int status;
 	int fd;