hwmon: (jc42) Add support for Microchip MCP9808 temperature sensor

MCP9808 is not officially compliant to JC-42, similar to MCP9804,
but its registers are compatible to JC-42.

Signed-off-by: Alison Schofield <amsfield22@gmail.com>
Cc: Daniel Baluta <daniel.baluta@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>