drm/msm: Correctly retrieve gpu's active power level

The parsing logic wrongly assumes the position of the initial/active power
level value in the gpu dts file. This leads to the active power level
always defaulting to a value of 1. Look for the initial power level
one level up in the device tree.

Change-Id: I63f8c8efd05ad3693c6f399f58bed44ac84105d2
Signed-off-by: Sharat Masetty <smasetty@codeaurora.org>