MAINTAINERS: Update Samsung pin control entry

Update to reflect the recent file movement to a sub-directory.

Signed-off-by: Sachin Kamat <sachin.kamat@samsung.com>
Acked-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>