media: MAINTAINERS: fix reference to STI CEC driver

STI CEC driver has move from staging directory to media/platform/sti/cec/

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>