[media] cobalt: fix 64-bit division

There are still some 64-bit division problems in the cobalt code.
Replace it by div_u64.

[mchehab@osg.samsung.com: folded with an additional diff sent by
 Hans via a priv e-mail]
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reported-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>