mmc: core: Calculate size from pointer

Calculate the size from pointer instead of
struct to adhere to linux kernel coding style.

Issue reported by checkpatch.

This commit has no functional changes.

Signed-off-by: Riyan Dhiman <riyandhiman14@gmail.com>
Link: https://lore.kernel.org/r/20240901173309.7124-1-riyandhiman14@gmail.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Author: Ryand1234

drivers/mmc/core/block.c

@@ -2530,7 +2530,7 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
 		return ERR_PTR(devidx);
 	}
 
-	md = kzalloc(sizeof(struct mmc_blk_data), GFP_KERNEL);
+	md = kzalloc(sizeof(*md), GFP_KERNEL);
 	if (!md) {
 		ret = -ENOMEM;
 		goto out;