mmc: fix integer assignments to pointer

Fix the sparse warning output "warning: Using plain integer as NULL pointer"

Signed-off-by: Venkatraman S <svenkatr@ti.com>
Signed-off-by: Chris Ball <cjb@laptop.org>
diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index 4c1a648..9b90726 100644
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -291,7 +291,7 @@
 	struct mmc_card *card;
 	struct mmc_command cmd = {0};
 	struct mmc_data data = {0};
-	struct mmc_request mrq = {0};
+	struct mmc_request mrq = {NULL};
 	struct scatterlist sg;
 	int err;
 
@@ -466,7 +466,7 @@
 	u32 result;
 	__be32 *blocks;
 
-	struct mmc_request mrq = {0};
+	struct mmc_request mrq = {NULL};
 	struct mmc_command cmd = {0};
 	struct mmc_data data = {0};
 	unsigned int timeout_us;