of_match_device could return NULL, and so cause a NULL pointer
dereference later at line 199:
priv->flags = of_id->data;

Reported-by: coverity (CID 1324140)
Signed-off-by: LABBE Corentin <clabbe.montjoie@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>