hvc_rtas_init() must be __init

This patch fixes the following section mismatch:

<-- snip -->

...
WARNING: vmlinux.o(.text+0x2fbca8): Section mismatch in reference from the function .hvc_rtas_init() to the function .devinit.text:.hvc_alloc()
...

<-- snip -->

---
1cc00c4ad5c881db2fc256ced43f3b5ce5c76e1c

index bb09413..88590d0 100644
@@ -76,7 +76,7 @@ static struct hv_ops hvc_rtas_get_put_ops = {
 	.put_chars = hvc_rtas_write_console,
 };
 
-static int hvc_rtas_init(void)
+static int __init hvc_rtas_init(void)
 {
 	struct hvc_struct *hp;