mmc: bcm2835: Fix dma_unmap_sg() nents value

The dma_unmap_sg() functions should be called with the same nents as the
dma_map_sg(), not the value the map function returned.

Fixes: 2f5da678351f ("mmc: bcm2835: Properly handle dmaengine_prep_slave_sg")
Signed-off-by: Thomas Fourier <[e-mail]>
Cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/mmc/host/bcm2835.c

···
 				       DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
 
 	if (!desc) {
-		dma_unmap_sg(dma_chan->device->dev, data->sg, sg_len, dir_data);
+		dma_unmap_sg(dma_chan->device->dev, data->sg, data->sg_len,
+			     dir_data);
 		return;
 	}