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 <[e-mail]>

drivers/mmc/host/wbsd.c

···
 
 	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;
···
 
 	host->dma = -1;
 	host->dma_buffer = NULL;
-	host->dma_addr = (dma_addr_t)NULL;
+	host->dma_addr = 0;
 }
 
 /*