mfd: exynos-lpass: Add missing remove() function

Disable device on driver remove and release allocated regmap.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Acked-for-MFD-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>