crypto: fix cppcheck warnings

sys/crypto/chacha.c

@@ -53,6 +53,8 @@ static void _doubleround(void *output_, const uint32_t input[16], uint8_t rounds
 
     rounds *= 4;
     for (unsigned i = 0; i < rounds; ++i) {
+        /* cppcheck-suppress duplicateExpressionTernary
+         * (reason: Externally imported code beautification) */
         uint32_t *a = &output[((i + ((i & 4) ? 0 : 0)) & 3) + (4 * 0)];
         uint32_t *b = &output[((i + ((i & 4) ? 1 : 0)) & 3) + (4 * 1)];
         uint32_t *c = &output[((i + ((i & 4) ? 2 : 0)) & 3) + (4 * 2)];

sys/crypto/modes/cbc.c

@@ -58,7 +58,7 @@ int cipher_decrypt_cbc(cipher_t* cipher, uint8_t iv[16],
                        uint8_t* input, size_t length, uint8_t* output)
 {
     size_t offset = 0;
-    uint8_t* input_block, *output_block, *input_block_last, block_size;
+    uint8_t* input_block, *input_block_last, block_size;
 
 
     block_size = cipher_get_block_size(cipher);
@@ -69,7 +69,7 @@ int cipher_decrypt_cbc(cipher_t* cipher, uint8_t iv[16],
     input_block_last = iv;
     do {
         input_block = input + offset;
-        output_block = output + offset;
+        uint8_t *output_block = output + offset;
 
         if (cipher_decrypt(cipher, input_block, output_block) != 1) {
             return CIPHER_ERR_DEC_FAILED;