msm: kgsl: Remove the frequency stepping work-around

In older hardware variants while running at GPU frequency x,
there was a .5x-2x limitation on changing it while the GPU was
active.  Therefore all frequency changes were stepped to avoid
stability issues.  This limitation is no longer in effect, so
remove the work-around.

Change-Id: I9716ba4cb40148d4db5ac1478b512a93707d88a1
CRs-fixed: 598694
Signed-off-by: Lucille Sylvester <lsylvest@codeaurora.org>