sht3x_crc
sncrcpt1 = sht3x_crc(&buf[0],2);
sncrcpt2 = sht3x_crc(&buf[3],2);
testcrc = sht3x_crc(svalptr, 2);
uint8_t c = sht3x_crc(&buf[0], 2);
static uint8_t sht3x_crc(uint8_t *, size_t);