msm: kgsl: Change call timing to alleviate mutex contention

Finish the state transition in the _idle_check function before
calling to update devfreq.  With this reordering the devfreq
notifier won't be stalled waiting for the GPU's device mutex.

Change-Id: I887d9b9d67292b0526de8f9692ff9f210a189fa5
Signed-off-by: Lucille Sylvester <lsylvest@codeaurora.org>