Using div_u64() instead of do_div() makes the code slightly more
readable by humans.

[mchehab@osg.samsung.org: originally, this patch was proposed as a bug
 fix for a gcc bug. This was solved already, but it is still better to
 use div_u64, instead of do_div, so I'm applying it, removing the
 comments about the gcc bug]
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>