mmc: bcm2835: Take SWIOTLB memory size limitation into account

Make sure the sdhost driver doesn't use requests bigger than SWIOTLB
can handle.
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/bcm2835.c

@@ -1314,7 +1314,7 @@ static int bcm2835_add_host(struct bcm2835_host *host)
 	}
 
 	mmc->max_segs = 128;
-	mmc->max_req_size = 524288;
+	mmc->max_req_size = min_t(size_t, 524288, dma_max_mapping_size(dev));
 	mmc->max_seg_size = mmc->max_req_size;
 	mmc->max_blk_size = 1024;
 	mmc->max_blk_count =  65535;