The MCP4725 has a register offset '3' for reading DAC value compared to
'4' for MCP4726. Add dac_reg_offset variable to struct mcp4725_chip_info
to handle this difference.

Drop chip_id from struct mcp4725_chip_info as it is unused.
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://lore.kernel.org/r/20230903115548.59306-5-biju.das.jz@bp.renesas.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>