pinctrl: ralink: rt2880: add missing NULL check

Memory is being requested to the kernel but there is
a missing check for NULL. Hence, add it.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20201213161721.6514-5-sergio.paracuellos@gmail.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/ralink/pinctrl-rt2880.c

@@ -238,6 +238,8 @@ static int rt2880_pinmux_index(struct rt2880_priv *p)
 			p->func[c] = &p->groups[i].func[j];
 			p->func[c]->groups = devm_kzalloc(p->dev, sizeof(int),
 						    GFP_KERNEL);
+			if (!p->func[c]->groups)
+				return -ENOMEM;
 			p->func[c]->groups[0] = i;
 			p->func[c]->group_count = 1;
 			c++;