MAINTAINERS: mfd: Cover MAX77843 by Maxim PMIC/MUIC for Exynos boards entry

The MAX77843 is used in Exynos5433-based TM2 boards and shares some
parts of code with MAX77693 (regulator and haptic motor drivers).
Include all MAX77843 drivers in the entry for Maxim PMIC/MUIC drivers
for Exynos boards, so they will receive some dedicated review coverage.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220111174805.223732-6-krzysztof.kozlowski@canonical.com