Fixed the value returned by sched_getaffinity().

On success gnu libc sched_getaffinity() should return 0, unlike underlying
Linux syscall which returns the size of CPU mask copied to user.

PR:		263939
MFC after:	2 weeks

lib/libc/gen/sched_getaffinity.c

@@ -39,9 +39,5 @@ sched_getaffinity(pid_t pid, size_t cpusetsz, cpuset_t *cpuset)
 	    pid == 0 ? -1 : pid, cpusetsz, cpuset);
 	if (error == -1 && errno == ERANGE)
 		errno = EINVAL;
-	if (error == 0)
-		return (cpusetsz < sizeof(cpuset_t) ? cpusetsz :
-		    sizeof(cpuset_t));
-
 	return (error);
 }