crypto: `memcpy()` in overlapping data in ccm

`memcpy()` must not be used if the input and output ranges overlap,
because it is undefined if the data if copied from front to the end or
vice versa.

Found via valgrind.

sys/crypto/modes/ccm.c

@@ -40,7 +40,7 @@ int ccm_compute_cbc_mac(cipher_t* cipher, uint8_t iv[16],
     uint8_t offset, block_size, mac_enc[16] = {0};
 
     block_size = cipher_get_block_size(cipher);
-    memcpy(mac, iv, 16);
+    memmove(mac, iv, 16);
     offset = 0;
     do {
         uint8_t block_size_input = (length - offset > block_size) ?