fbcon: when font is freed, clear also vc_font.data

commit ae128786
Author: Dave Airlie <airlied@redhat.com>
Date:   Thu Jan 24 16:12:41 2013 +1000

    fbcon: don't lose the console font across generic->chip driver switch

uses a pointer in vc->vc_font.data to load font into the new driver.
However if the font is actually freed, we need to clear the data
so that we don't reload font from dangling pointer.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=892340


Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>