iio:buffer: make length types match kfifo types

Currently, we use int for buffer length and bytes_per_datum. However,
kfifo uses unsigned int for length and size_t for element size. We need
to make sure these matches or we will have bugs related to overflow (in
the range between INT_MAX and UINT_MAX for length, for example).

In addition, set_bytes_per_datum uses size_t while bytes_per_datum is an
int, which would cause bugs for large values of bytes_per_datum.

Change buffer length to use unsigned int and bytes_per_datum to use
size_t.

Signed-off-by: Martin Kelly <mkelly@xevo.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
diff --git a/drivers/iio/buffer/industrialio-buffer-dma.c b/drivers/iio/buffer/industrialio-buffer-dma.c
index 05e0c35..b32bf57 100644
--- a/drivers/iio/buffer/industrialio-buffer-dma.c
+++ b/drivers/iio/buffer/industrialio-buffer-dma.c
@@ -587,7 +587,7 @@ EXPORT_SYMBOL_GPL(iio_dma_buffer_set_bytes_per_datum);
  * Should be used as the set_length callback for iio_buffer_access_ops
  * struct for DMA buffers.
  */
-int iio_dma_buffer_set_length(struct iio_buffer *buffer, int length)
+int iio_dma_buffer_set_length(struct iio_buffer *buffer, unsigned int length)
 {
 	/* Avoid an invalid state */
 	if (length < 2)