[ARM] Make sys_ipc return ENOSYS for unrecognised IPC calls.

arch/arm/kernel/sys_arm.c

@@ -229,7 +229,7 @@ asmlinkage int sys_ipc (uint call, int first, int second, int third, void *ptr,
 		return sys_shmctl (first, second,
 				   (struct shmid_ds *) ptr);
 	default:
-		return -EINVAL;
+		return -ENOSYS;
 	}
 }