msm: kgsl: set the correct max_state

Max_state from the driver should be set to the number of power
levels. The devfreq governor then checks the frequencies from
0 to max_state -1.

Change-Id: I79a6da698ff8bcb2840774ccc5d792b7ddbf126b
Signed-off-by: Suman Tatiraju <sumant@codeaurora.org>