media: tw686x: Fix incorrect vb2_mem_ops GFP flags

When the driver is configured in the "memcpy" dma-mode,
it uses vb2_vmalloc_memops, which is backed by a SLAB
allocator and so shouldn't be using GFP_DMA32.

Fix it.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>