mfd: max77693: Remove unused structures

The max77693 regulator driver no longer supports board files. Remove the
left-overs. Additionally fix name of device in comment.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>