cobalt: Fix error code of cobalt_thread_setschedparam_ex

This aligns the return code with cobalt_sched_setschedparam_ex: If there
is no u_winoff and no thread, we should return ESRCH so that userspace
can easily detect that it should call the standard libc service instead.
Fix the core and remove the related workaround from the userspace lib.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

kernel/cobalt/posix/thread.c

@@ -478,7 +478,7 @@ int cobalt_thread_setschedparam_ex(unsigned long pth,
 	thread = thread_lookup(&hkey);
 	if (thread == NULL) {
 		if (u_winoff == NULL)
-			return -EINVAL;
+			return -ESRCH;
 			
 		thread = cobalt_thread_shadow(&hkey, u_winoff);
 		if (IS_ERR(thread))

lib/cobalt/thread.c

@@ -648,7 +648,7 @@ int pthread_setschedparam_ex(pthread_t thread,
 	 * If the kernel has no reference to the target thread. let glibc
 	 * handle the call.
 	 */
-	if (!u_winoff_ptr && ret == EINVAL) {
+	if (ret == ESRCH) {
 		std_policy = cobalt_xlate_schedparam(policy, param_ex,
 						     &std_param);
 		return __STD(pthread_setschedparam(thread, std_policy,