mfd: bcm590xx: Simplify a test

'i2c_new_dummy()' does not return an error pointer, so the test can be
simplified to be more consistent.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/bcm590xx.c

@@ -67,7 +67,7 @@ static int bcm590xx_i2c_probe(struct i2c_client *i2c_pri,
 	/* Secondary I2C slave address is the base address with A(2) asserted */
 	bcm590xx->i2c_sec = i2c_new_dummy(i2c_pri->adapter,
 					  i2c_pri->addr | BIT(2));
-	if (IS_ERR_OR_NULL(bcm590xx->i2c_sec)) {
+	if (!bcm590xx->i2c_sec) {
 		dev_err(&i2c_pri->dev, "failed to add secondary I2C device\n");
 		return -ENODEV;
 	}