pseries: Check we have a chardev in spapr_vty_init()

If qemu is run like:

 qemu-system-ppc64 -nodefaults -device spapr-vty

We end up in spapr_vty_init() with dev->chardev == NULL. Currently
that leads to a segfault because we unconditionally call
qemu_chr_add_handlers().

Although we could make that call conditional, I think a spapr-vty
without a chardev is basically useless so fail the init. This is
similar to what the serial code does for example.
Signed-off-by: NMichael Ellerman <michael@ellerman.id.au>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NAlexander Graf <agraf@suse.de>

hw/spapr_vty.c

@@ -58,6 +58,11 @@ static int spapr_vty_init(VIOsPAPRDevice *sdev)
 {
     VIOsPAPRVTYDevice *dev = (VIOsPAPRVTYDevice *)sdev;
 
+    if (!dev->chardev) {
+        fprintf(stderr, "spapr-vty: Can't create vty without a chardev!\n");
+        exit(1);
+    }
+
     qemu_chr_add_handlers(dev->chardev, vty_can_receive,
                           vty_receive, NULL, dev);