crypto: tcrypt - do not attempt to write to readonly variable

Commit da7f033ddc (”crypto: cryptomgr - Add test infrastructure”) added a
const to variable which is later used as target buffer of memcpy.

crypto/tcrypt.c:217:12: warning: passing 'const char (*)[128]' to parameter of type 'void *' discards qualifiers
                                memset(&iv, 0xff, iv_len);


crypto/tcrypt.c:test_cipher_speed()

-       unsigned char *key, iv[128];
+       const char *key, iv[128];
...
        memset(&iv, 0xff, iv_len);

Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/tcrypt.c

@@ -146,7 +146,8 @@ static void test_cipher_speed(const char *algo, int enc, unsigned int sec,
 			      unsigned int tcount, u8 *keysize)
 {
 	unsigned int ret, i, j, iv_len;
-	const char *key, iv[128];
+	const char *key;
+	char iv[128];
 	struct crypto_blkcipher *tfm;
 	struct blkcipher_desc desc;
 	const char *e;