selftests/capabilities: fix warn_unused_result build warnings

Fix the following warnings by adding return check and error handling.

test_execve.c: In function ‘do_tests’:
test_execve.c:100:17: warning: ignoring return value of
‘capng_get_caps_process’
declared with attribute ‘warn_unused_result’ [-Wunused-result]
100 | capng_get_caps_process();
| ^~~~~~~~~~~~~~~~~~~~~~~~
validate_cap.c: In function ‘main’:
validate_cap.c:47:9: warning: ignoring return value of
‘capng_get_caps_process’
declared with attribute ‘warn_unused_result’ [-Wunused-result]
47 | capng_get_caps_process();
| ^~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Amer Al Shanawany <[e-mail]>
Reviewed-by: Muhammad Usama Anjum <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/capabilities/test_execve.c

···
 {
 	uid_t outer_uid;
 	gid_t outer_gid;
-	int i;
+	int i, ret;
 	bool have_outer_privilege;
 
 	outer_uid = getuid();
···
 			ksft_exit_fail_msg("setresuid - %s\n", strerror(errno));
 
 		// Re-enable effective caps
-		capng_get_caps_process();
+		ret = capng_get_caps_process();
+		if (ret == -1)
+			ksft_exit_fail_msg("capng_get_caps_process failed\n");
+
 		for (i = 0; i < CAP_LAST_CAP; i++)
 			if (capng_have_capability(CAPNG_PERMITTED, i))
 				capng_update(CAPNG_ADD, CAPNG_EFFECTIVE, i);
···
 
 static int do_tests(int uid, const char *our_path)
 {
+	int ret;
 	bool have_outer_privilege = create_and_enter_ns(uid);
 
 	int ourpath_fd = open(our_path, O_RDONLY | O_DIRECTORY);
···
 			ksft_exit_fail_msg("chmod - %s\n", strerror(errno));
 	}
 
-	capng_get_caps_process();
+	ret = capng_get_caps_process();
+	if (ret == -1)
+		ksft_exit_fail_msg("capng_get_caps_process failed\n");
 
 	/* Make sure that i starts out clear */
 	capng_update(CAPNG_DROP, CAPNG_INHERITABLE, CAP_NET_BIND_SERVICE);

tools/testing/selftests/capabilities/validate_cap.c

···
 int main(int argc, char **argv)
 {
 	const char *atsec = "";
+	int ret;
 
 	/*
 	 * Be careful just in case a setgid or setcapped copy of this
···
 		atsec = " (AT_SECURE is not set)";
 #endif
 
-	capng_get_caps_process();
+	ret = capng_get_caps_process();
+	if (ret == -1) {
+		ksft_print_msg("capng_get_caps_process failed\n");
+		return 1;
+	}
 
 	if (capng_have_capability(CAPNG_EFFECTIVE, CAP_NET_BIND_SERVICE) != bool_arg(argv, 1)) {
 		ksft_print_msg("Wrong effective state%s\n", atsec);