media: vivid: drop GFP_DMA32

>From what I can see, this is not needed. And since using it issues a 'deprecated'
warning, just drop it.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>