media: raspberrypi: cfe: Fix mapping of dmabuf buffers

When using buffers from DRM, DMA-API gives a warning about: "mapping sg
segment longer than device claims to support [len=307200] [max=65536]"

Add a call to vb2_dma_contig_set_max_seg_size() to tell the DMA-API
about the supported segment size (which is UINT_MAX).

Fixes: 6edb685a ("media: raspberrypi: Add support for RP1-CFE")
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>