use 20kHz as I2C frequency

[rsbs2] / src / rsb-crc.h

unsigned int rsb_crc(unsigned int r11_crc, unsigned char *r10_buf, unsigned int r14_len);
unsigned int rsb_crc2(unsigned char *r0_buf, unsigned int r1_buflen, unsigned int r2_magic, unsigned int *crc_out);