msm: kgsl: Clean up power-related members if probe fails

If power-related initialization fails during device probe, clean up
the kgsl structure members. This is useful if the device probe is
retried later.

Change-Id: I75aeb199da685bb5055ba5a8a0bb552656951674
Signed-off-by: Lynus Vaz <lvaz@codeaurora.org>