spi: spidev: use memdup_user

Use memdup_user() helper instead of open-coding to simplify the code.
Signed-off-by: Geliang Tang <geliangtang@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spidev.c

@@ -324,7 +324,6 @@ static struct spi_ioc_transfer *
 spidev_get_ioc_message(unsigned int cmd, struct spi_ioc_transfer __user *u_ioc,
 		unsigned *n_ioc)
 {
-	struct spi_ioc_transfer	*ioc;
 	u32	tmp;
 
 	/* Check type, command number and direction */
@@ -341,14 +340,7 @@ spidev_get_ioc_message(unsigned int cmd, struct spi_ioc_transfer __user *u_ioc,
 		return NULL;
 
 	/* copy into scratch area */
-	ioc = kmalloc(tmp, GFP_KERNEL);
-	if (!ioc)
-		return ERR_PTR(-ENOMEM);
-	if (__copy_from_user(ioc, u_ioc, tmp)) {
-		kfree(ioc);
-		return ERR_PTR(-EFAULT);
-	}
-	return ioc;
+	return memdup_user(u_ioc, tmp);
 }
 
 static long