drm/vkms: Fix plane duplicate_state

drm/vkms: Fix plane duplicate_state

commit 7cdf33ab02e01300e7e6289acbac9cd8759f8712 upstream.

We need to handle allocation failures and bail out. While at it, tune
the allocation failures down to debug level.

syzbot injected an allocation failure and then hit this WARN_ON.

Reported-by: syzbot+eb6e5365f23c02517dda@syzkaller.appspotmail.com
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Cc: Gustavo Padovan <gustavo.padovan@collabora.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20181128101033.4840-1-daniel.vetter@ffwll.ch
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>