exynos: update maintainer of Snow and SMDK5420 board

The email address of Rajeshwari Shinde <rajeshwari.s@samsung.com>
is not working.

This commit gives Akshay the maintainership of Snow and
SMDK5420 boards.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Akshay Saraswat <akshay.s@samsung.com>
Cc: Minkyu Kang <mk7.kang@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>