console: Preserve index after console setup()

Before register_console() calls the setup() method of the matched
console, the registering console index is already equal to the index
from the console command line; ie. newcon->index == c->index.

This change is also required to support extensible console matching;
(the command line index may have no relation to the console index
assigned by the console-defined match() function).

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>