nuttx/sched: Remove explicit references to errno. That is a problem from within the kernel for certain configurations

sched/environ/env_putenv.c

@@ -113,7 +113,7 @@ int putenv(FAR const char *string)
   return ret;
 
 errout:
-  errno = ret;
+  set_errno(ret);
   return ERROR;
 }
 

sched/environ/env_setenv.c

@@ -197,7 +197,7 @@ int setenv(FAR const char *name, FAR const char *value, int overwrite)
 errout_with_lock:
   sched_unlock();
 errout:
-  errno = ret;
+  set_errno(ret);
   return ERROR;
 }