drm/vc4: Fix OOPSes from trying to cache a partially constructed BO.

drm/vc4: Fix OOPSes from trying to cache a partially constructed BO.

commit ca39b449f6d03e8235969f12f5dd25b8eb4304d6 upstream.

If a CMA allocation failed, the partially constructed BO would be
unreferenced through the normal path, and we might choose to put it in
the BO cache.  If we then reused it before it expired from the cache,
the kernel would OOPS.

Signed-off-by: Eric Anholt <eric@anholt.net>
Fixes: c826a6e10644 ("drm/vc4: Add a BO cache.")
Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170301185602.6873-2-eric@anholt.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>