soc: bcm: Check for NULL return of devm_kzalloc()

As the potential failure of allocation, devm_kzalloc() may return NULL.  Then
the 'pd->pmb' and the follow lines of code may bring null pointer dereference.

Therefore, it is better to check the return value of devm_kzalloc() to avoid
this confusion.

Fixes: 8bcac4011e ("soc: bcm: add PM driver for Broadcom's PMB")
Signed-off-by: QintaoShen <unSimple1993@163.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

drivers/soc/bcm/bcm63xx/bcm-pmb.c

@@ -312,6 +312,9 @@ static int bcm_pmb_probe(struct platform_device *pdev)
 	for (e = table; e->name; e++) {
 		struct bcm_pmb_pm_domain *pd = devm_kzalloc(dev, sizeof(*pd), GFP_KERNEL);
 
+		if (!pd)
+			return -ENOMEM;
+
 		pd->pmb = pmb;
 		pd->data = e;
 		pd->genpd.name = e->name;