media: MAINTAINERS: adjust entries to moving CEC USB drivers

Commit a8106818 ("media: move CEC USB drivers to a separate directory")
moved drivers/media/usb/{pulse8,rainshadow}-cec to
drivers/media/cec/usb/{rainshadow,pulse8}, but did not adjust the entries
in MAINTAINERS.

Since then, ./scripts/get_maintainer.pl --self-test=patterns complains:

  warning: no file matches F: drivers/media/usb/pulse8-cec/*
  warning: no file matches F: drivers/media/usb/rainshadow-cec/*

Update the MAINTAINERS entries to the new file locations.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>