wbsd: fix bad dma_addr_t conversion

DMA addresses are not pointers, so don't treat them as such. Avoids
compiler warnings when using 64-bit DMA addresses on a 32-bit system.

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>
diff --git a/drivers/mmc/host/wbsd.c b/drivers/mmc/host/wbsd.c
index c2b6160..f7dcd8e 100644
--- a/drivers/mmc/host/wbsd.c
+++ b/drivers/mmc/host/wbsd.c
@@ -1420,7 +1420,7 @@
 
 	dma_unmap_single(mmc_dev(host->mmc), host->dma_addr,
 		WBSD_DMA_SIZE, DMA_BIDIRECTIONAL);
-	host->dma_addr = (dma_addr_t)NULL;
+	host->dma_addr = 0;
 
 	kfree(host->dma_buffer);
 	host->dma_buffer = NULL;
@@ -1445,7 +1445,7 @@
 
 	host->dma = -1;
 	host->dma_buffer = NULL;
-	host->dma_addr = (dma_addr_t)NULL;
+	host->dma_addr = 0;
 }
 
 /*