media: vimc: zero the media_device on probe

The media_device is part of a static global vimc_device struct.
The media framework expects this to be zeroed before it is
used, however, since this is a global this is not the case if
vimc is unbound and then bound again.

So call memset to ensure any left-over values are cleared.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>