mfd: max5970: Rename driver and remove wildcard

The previous version of this driver included wildcards in file names
and descriptions. This patch renames the driver to only support MAX5970
and MAX5978, which are the only chips that the driver actually supports.

Signed-off-by: Naresh Solanki <Naresh.Solanki@9elements.com>
Link: https://lore.kernel.org/r/20230427113046.3971425-1-Naresh.Solanki@9elements.com
Signed-off-by: Lee Jones <lee@kernel.org>