MAINTAINERS: mmc: Add Jaehoon as co-maintainer for SDHCI SAMSUNG DRIVER

Jaehoon has volunteered in maintaining the SDHCI SAMSUNG DRIVER so
add him.

Since we are updating this section let's also correct file path to
cover all files for sdhci-s3c.

Cc: Ben Dooks <ben-linux@fluff.org>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>