powerpc/hvsi: Avoid calculating possibly-invalid address

Check whether index is within bounds prior to calculating a
possibly-invalid address.
Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Cc: Bernd Petrovitsch <bernd@firmix.at>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

drivers/char/hvsi.c

@@ -1230,11 +1230,12 @@ static struct tty_driver *hvsi_console_device(struct console *console,
 
 static int __init hvsi_console_setup(struct console *console, char *options)
 {
-	struct hvsi_struct *hp = &hvsi_ports[console->index];
+	struct hvsi_struct *hp;
 	int ret;
 
 	if (console->index < 0 || console->index >= hvsi_count)
 		return -1;
+	hp = &hvsi_ports[console->index];
 
 	/* give the FSP a chance to change the baud rate when we re-open */
 	hvsi_close_protocol(hp);