mfd: iqs62x: Rename regmap_config struct

The regmap member of the driver's private data is called 'regmap',
but the regmap_config struct is called 'iqs62x_map_config'. Rename
the latter to 'iqs62x_regmap_config' for consistency.

Signed-off-by: Jeff LaBundy <jeff@labundy.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>