rockchip: Add MAINTAINER entry for chromebook_speedy
This adds a MAINTAINER entry for chromebook_speedy.
Without this, we get the following warnings from the maintainers
check:
WARNING: no status info for 'chromebook_minnie'
WARNING: no maintainers for 'chromebook_minnie'
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>