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/ulimit/ulimit01.c b/testcases/kernel/syscalls/ulimit/ulimit01.c
index 484f9c8..2ce5cfa 100644
--- a/testcases/kernel/syscalls/ulimit/ulimit01.c
+++ b/testcases/kernel/syscalls/ulimit/ulimit01.c
@@ -155,7 +155,7 @@
 {
 	int lc;
 	int i;
-	char *msg;
+	const char *msg;
 	int tmp;
 
 	TST_TOTAL = sizeof(Scenarios) / sizeof(struct limits_t);