irqchip/irq-qcom-mpm: fix return value check in qcom_mpm_init()

If devm_platform_ioremap_resource() fails, it never returns
NULL, replace NULL check with IS_ERR().

Fixes: a6199bb514d8 ("irqchip: Add Qualcomm MPM controller driver")
Reported-by: Hulk Robot <[e-mail]>
Signed-off-by: Yang Yingliang <[e-mail]>
Acked-by: Shawn Guo <[e-mail]>
Signed-off-by: Marc Zyngier <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/irqchip/irq-qcom-mpm.c

···
 	raw_spin_lock_init(&priv->lock);
 
 	priv->base = devm_platform_ioremap_resource(pdev, 0);
-	if (!priv->base)
+	if (IS_ERR(priv->base))
 		return PTR_ERR(priv->base);
 
 	for (i = 0; i < priv->reg_stride; i++) {