drm/tinydrm: Use kmemdup rather than duplicating its implementation in repaper_spi_transfer()

use kmemdup rather than duplicating its implementation
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1543471233-159568-1-git-send-email-yuehaibing@huawei.com

drivers/gpu/drm/tinydrm/repaper.c

@@ -108,12 +108,11 @@ static int repaper_spi_transfer(struct spi_device *spi, u8 header,
 
 	/* Stack allocated tx? */
 	if (tx && len <= 32) {
-		txbuf = kmalloc(len, GFP_KERNEL);
+		txbuf = kmemdup(tx, len, GFP_KERNEL);
 		if (!txbuf) {
 			ret = -ENOMEM;
 			goto out_free;
 		}
-		memcpy(txbuf, tx, len);
 	}
 
 	if (rx) {