mtd: rawnand: Add status chack in r852_ready()

commit b79fe1829975556854665258cf4d2476784a89db upstream.

In r852_ready(), the dev get from r852_get_dev() need to be checked.
An unstable device should not be ready. A proper implementation can
be found in r852_read_byte(). Add a status check and return 0 when it is
unstable.

Fixes: 50a487e7 ("mtd: rawnand: Pass a nand_chip object to chip->dev_ready()")
Cc: stable@vger.kernel.org # v4.20+
Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>