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>
diff --git a/drivers/mfd/bcm590xx.c b/drivers/mfd/bcm590xx.c
index 0d76d69..c572a35 100644
--- a/drivers/mfd/bcm590xx.c
+++ b/drivers/mfd/bcm590xx.c
@@ -67,7 +67,7 @@
 	/* 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;
 	}