iio: buffer-dma: Use round_down() instead of rounddown()

We know that the buffer's alignment will always be a power of two;
therefore, we can use the faster round_down() macro.
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Link: https://lore.kernel.org/r/20211115141925.60164-4-paul@crapouillou.netSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/buffer/industrialio-buffer-dmaengine.c

@@ -67,7 +67,7 @@ static int iio_dmaengine_buffer_submit_block(struct iio_dma_buffer_queue *queue,
 	dma_cookie_t cookie;
 
 	block->bytes_used = min(block->size, dmaengine_buffer->max_size);
-	block->bytes_used = rounddown(block->bytes_used,
+	block->bytes_used = round_down(block->bytes_used,
 			dmaengine_buffer->align);
 
 	desc = dmaengine_prep_slave_single(dmaengine_buffer->chan,