Fix compile warning in test_execve.c.

diff --git a/tools/testing/selftests/capabilities/test_execve.c b/tools/testing/selftests/capabilities/test_execve.c
--- a/tools/testing/selftests/capabilities/test_execve.c
+++ b/tools/testing/selftests/capabilities/test_execve.c
@@ -91,7 +91,7 @@ static bool create_and_enter_ns(uid_t inner_uid)
 	uid_t outer_uid;
 	gid_t outer_gid;
 	int i;
-	bool have_outer_privilege;
+	bool have_outer_privilege = false;
 
 	outer_uid = getuid();
 	outer_gid = getgid();