crypto: omap-des - handle NULL cipher request

If no data is provided for DES request, just return immediately. No
processing is needed in this case.

Signed-off-by: Tero Kristo <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

drivers/crypto/omap-des.c

···
 		 !!(mode & FLAGS_ENCRYPT),
 		 !!(mode & FLAGS_CBC));
 
+	if (!req->cryptlen)
+		return 0;
+
 	if (!IS_ALIGNED(req->cryptlen, DES_BLOCK_SIZE))
 		return -EINVAL;