media: vivid: fix incorrect assignment operation when setting video mode

The assigment of FB_VMODE_NONINTERLACE to var->vmode should be a
bit-wise or of FB_VMODE_NONINTERLACE instead of an assignment,
otherwise the previous clearing of the FB_VMODE_MASK bits of
var->vmode makes no sense and is redundant.

Addresses-Coverity: ("Unused value")
Fixes: ad4e02d5 ("[media] vivid: add a simple framebuffer device for overlay testing")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>