media: vidtv: use a simpler name in platform_{device|driver}

Change from "vidtv_bridge" to simply "vidtv" so that vidtv looks
more similar to the other media virtual drivers in /sys/bus/platform.

Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>