mmc: core: Use memdup_user() rather than duplicating its implementation

Reuse existing functionality from memdup_user() instead of keeping
duplicate source code.

This issue was detected by using the Coccinelle software.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/block.c

@@ -375,22 +375,15 @@ static struct mmc_blk_ioc_data *mmc_blk_ioctl_copy_from_user(
 		return idata;
 	}
 
-	idata->buf = kmalloc(idata->buf_bytes, GFP_KERNEL);
-	if (!idata->buf) {
-		err = -ENOMEM;
+	idata->buf = memdup_user((void __user *)(unsigned long)
+				 idata->ic.data_ptr, idata->buf_bytes);
+	if (IS_ERR(idata->buf)) {
+		err = PTR_ERR(idata->buf);
 		goto idata_err;
 	}
 
-	if (copy_from_user(idata->buf, (void __user *)(unsigned long)
-					idata->ic.data_ptr, idata->buf_bytes)) {
-		err = -EFAULT;
-		goto copy_err;
-	}
-
 	return idata;
 
-copy_err:
-	kfree(idata->buf);
 idata_err:
 	kfree(idata);
 out: