[libc] Correct standard for getcpu (#153982)

libc/include/sched.yaml

diff --git a/libc/include/sched.yaml b/libc/include/sched.yaml
index f14799d..8014aa7 100644
--- a/libc/include/sched.yaml
+++ b/libc/include/sched.yaml
@@ -20,7 +20,7 @@
       - type: const cpu_set_t *
   - name: getcpu
     standards:
-      - POSIX
+      - Linux
     return_type: int
     arguments:
       - type: unsigned int *