drm/nouveau: fix for disabled fbdev emulation

drm/nouveau: fix for disabled fbdev emulation

Hello,

after this commit:

commit 1dd6391afc6632ac8b6d6c8d59f6945fc99d89e3
Author: Ben Skeggs <bskeggs@redhat.com>
Date:   Thu Jun 2 12:23:31 2016 +1000
    drm/nouveau/fbcon: fix out-of-bounds memory accesses

kernel started to oops when loading nouveau module when using GTX 780 Ti
video adapter. This patch fixes the problem.

Bug report: https://bugzilla.kernel.org/show_bug.cgi?id=120591

Signed-off-by: Dmitrii Tcvetkov <demfloro@demfloro.ru>
Suggested-by: Ilia Mirkin <imirkin@alum.mit.edu>
Fixes: 1dd6391afc66 ("nouveau_fbcon_init()")
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Cc: stable@vger.kernel.org