mmc: block: return error on failed mmc_blk_get()

This used to return -EFAULT, but the function above returns -EINVAL on
the same condition so let's stick to that.

The removal of error return on this path was introduced with b093410c
('mmc: block: copy resp[] data on err for MMC_IOC_MULTI_CMD').

Fixes: b093410c ('mmc: block: copy resp[] data on err for MMC_IOC_MULTI_CMD').
Signed-off-by: NOlof Johansson <olof@lixom.net>
Cc: Grant Grundler <grundler@google.com>
Signed-off-by: NUlf Hansson <ulf.hansson@linaro.org>

drivers/mmc/card/block.c

@@ -655,8 +655,10 @@ static int mmc_blk_ioctl_multi_cmd(struct block_device *bdev,
 	}
 
 	md = mmc_blk_get(bdev->bd_disk);
-	if (!md)
+	if (!md) {
+		err = -EINVAL;
 		goto cmd_err;
+	}
 
 	card = md->queue.card;
 	if (IS_ERR(card)) {