iio: adc: xilinx: use devm_krealloc() instead of kfree() + kcalloc()

We now have devm_krealloc() in the kernel Use it indstead of calling
kfree() and kcalloc() separately.
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Tested-by: Anand Ashok Dumbre <anandash@xilinx.com>
Reviewed-by: Anand Ashok Dumbre <anandash@xilinx.com>
Link: https://lore.kernel.org/r/20201130142759.28216-3-brgl@bgdev.plSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/xilinx-xadc-core.c

@@ -19,6 +19,7 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/of.h>
+#include <linux/overflow.h>
 #include <linux/platform_device.h>
 #include <linux/slab.h>
 #include <linux/sysfs.h>
@@ -610,15 +611,22 @@ static int xadc_update_scan_mode(struct iio_dev *indio_dev,
 	const unsigned long *mask)
 {
 	struct xadc *xadc = iio_priv(indio_dev);
-	unsigned int n;
+	size_t new_size, n;
+	void *data;
 
 	n = bitmap_weight(mask, indio_dev->masklength);
 
-	kfree(xadc->data);
-	xadc->data = kcalloc(n, sizeof(*xadc->data), GFP_KERNEL);
-	if (!xadc->data)
+	if (check_mul_overflow(n, sizeof(*xadc->data), &new_size))
+		return -ENOMEM;
+
+	data = devm_krealloc(indio_dev->dev.parent, xadc->data,
+			     new_size, GFP_KERNEL);
+	if (!data)
 		return -ENOMEM;
 
+	memset(data, 0, new_size);
+	xadc->data = data;
+
 	return 0;
 }
 
@@ -1473,7 +1481,6 @@ static int xadc_remove(struct platform_device *pdev)
 	free_irq(xadc->irq, indio_dev);
 	cancel_delayed_work_sync(&xadc->zynq_unmask_work);
 	clk_disable_unprepare(xadc->clk);
-	kfree(xadc->data);
 
 	return 0;
 }