mfd: lpc_ich: Make struct lpc_ich_priv use enum for chipset member

We have a specific enum for the supported chipsets.
Make struct lpc_ich_priv use better type for the chipset member.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230926190834.932233-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Lee Jones <lee@kernel.org>