[media] videobuf2-dma-contig: make cookie() return a pointer to dma_addr_t

dma_addr_t may not fit into void* on some architectures. To be safe, make
vb2_dma_contig_cookie() return a pointer to dma_addr_t and dereference it
in vb2_dma_contig_plane_paddr() back to dma_addr_t.

Signed-off-by: Pawel Osciak <pawel@osciak.com>
Reported-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>