MAINTAINERS: move the staging subsystem to lists.linux.dev

MAINTAINERS: move the staging subsystem to lists.linux.dev

The drivers/staging/ tree has a new mailing list,
linux-staging@lists.linux.dev, so move the MAINTAINER entry to point to
it so that we get patches sent to the proper place.

There was no need to specify a list for the hikey9xx driver, the tools
pick up the "base" list for drivers/staging/* so remove that line to
make the file simpler.

Cc: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/20210316102311.182375-1-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>