Use XOR instead of AND operation when calculating CRC

[xy007man]

crc_t crc_update(crc_t crc, const void *data, size_t data_len)
{
const unsigned char *d = (const unsigned char *)data;
unsigned int tbl_idx;

while (data_len--) {
    tbl_idx = crc ^ *d;
    crc = crc_table[tbl_idx] & 0xff;
    d++;
}
return crc & 0xff; ==> crc ^ 0xff

}