drm: don't check modeset locks in panic handler

Since we know that locking is broken in that case and it's more
important to not flood the dmesg with random gunk.

Cc: Dave Airlie <airlied@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>
References: http://lkml.kernel.org/r/20130502000206.GH15623@pd.tnic


Cc: stable@vger.kernel.org
Reported-and-tested-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>