devfreq: Fix 64-bit div compilation issue

Currently 32-bit div() is used on a 64-bit data which can truncate
the data. Fix this by using 64-bit division macro.

Change-Id: Icfde1182bfd5b9d9ea855da1e341913900e91f65
Signed-off-by: Biao Long <blong@codeaurora.org>