msm: kgsl: Always go to max clock rate on a pwrscale policy change

Especially when setting the policy to "none" we want to end up at the
highest frequency, rather than a random frequency.

Change-Id: I845a205be04482099ae3dafd13fdc55c63b7d952
Signed-off-by: Lucille Sylvester <lsylvest@codeaurora.org>