s390/crypto: unlock on error in prng_tdes_read()

We added some new locking but forgot to unlock on error.

Fixes: 57127645d7 ("s390/zcrypt: Introduce new SHA-512 based Pseudo Random Generator.")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/crypto/prng.c

@@ -507,8 +507,10 @@ static ssize_t prng_tdes_read(struct file *file, char __user *ubuf,
 		prng_data->prngws.byte_counter += n;
 		prng_data->prngws.reseed_counter += n;
 
-		if (copy_to_user(ubuf, prng_data->buf, chunk))
-			return -EFAULT;
+		if (copy_to_user(ubuf, prng_data->buf, chunk)) {
+			ret = -EFAULT;
+			break;
+		}
 
 		nbytes -= chunk;
 		ret += chunk;