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