xen/hvc: allow xenboot console to be used again

Commit d0380e6 (early_printk:
consolidate random copies of identical code) added in 3.10 introduced
a check for con->index == -1 in early_console_register().

Initialize index to -1 for the xenboot console so earlyprintk=xen
works again.

Signed-off-by: David Vrabel <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Jiri Slaby <[email protected]>
Cc: [email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: David Vrabel

drivers/tty/hvc/hvc_xen.c

@@ -636,6 +636,7 @@ struct console xenboot_console = {
 	.name		= "xenboot",
 	.write		= xenboot_write_console,
 	.flags		= CON_PRINTBUFFER | CON_BOOT | CON_ANYTIME,
+	.index		= -1,
 };
 #endif	/* CONFIG_EARLY_PRINTK */