Fix warning about missing return value

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5405 c046a42c-6fe2-441c-8c8c-71466251a162

block-raw-posix.c

@@ -748,6 +748,7 @@ static void raw_aio_cancel(BlockDriverAIOCB *blockacb)
 #else /* CONFIG_AIO */
 static int posix_aio_init(void)
 {
+    return 0;
 }
 #endif /* CONFIG_AIO */