Function devm_gpiod_get_optional() returns an ERR_PTR on failure. Its
return value should not be validated by a NULL check. Instead, use IS_ERR.
Signed-off-by: NPan Bian <bianpan2016@163.com>
Reviewed-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>