mmc: core: Handle card shutdown from mmc_bus

Considering shutdown of the card, the responsibility to initate this
sequence shall be driven from the mmc_bus.

This patch enables the mmc_bus to handle this sequence properly. A new
.shutdown callback is added in the mmc_driver struct which is used to
shutdown the blk device.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>
diff --git a/drivers/mmc/card/mmc_test.c b/drivers/mmc/card/mmc_test.c
index 759714e..a69df52 100644
--- a/drivers/mmc/card/mmc_test.c
+++ b/drivers/mmc/card/mmc_test.c
@@ -3025,12 +3025,17 @@
 	mmc_test_free_dbgfs_file(card);
 }
 
+static void mmc_test_shutdown(struct mmc_card *card)
+{
+}
+
 static struct mmc_driver mmc_driver = {
 	.drv		= {
 		.name	= "mmc_test",
 	},
 	.probe		= mmc_test_probe,
 	.remove		= mmc_test_remove,
+	.shutdown	= mmc_test_shutdown,
 };
 
 static int __init mmc_test_init(void)