media: zoran: use u64 for the timestamp internally

Just like vb2 does, use u64 internally to store the timestamps
of the buffers. Only convert to timeval when interfacing with
userspace.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>