mfd: ab8500-debugfs: Apply a check for -ENOMEM after allocating memory for sysfs

The AB8500 debugfs driver allocates memory for a new sysfs entry, but
fails to apply the proper post-allocation checks. If the device were to
run out of memory, the allocation would return NULL. Without the correct
checks the driver will continue to populate NULL->[show|store|...],
which would obviously cause a pointer dereference Oops.

Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/ab8500-debugfs.c

@@ -2800,6 +2800,9 @@ static ssize_t ab8500_subscribe_write(struct file *file,
 	 */
 	dev_attr[irq_index] = kmalloc(sizeof(struct device_attribute),
 		GFP_KERNEL);
+	if (!dev_attr[irq_index])
+		return -ENOMEM;
+
 	event_name[irq_index] = kmalloc(count, GFP_KERNEL);
 	sprintf(event_name[irq_index], "%lu", user_val);
 	dev_attr[irq_index]->show = show_irq;