msm: kgsl: Initialize drawctxt active node earlier

gpudev->preemption_context_init() can fail and invoke
adreno_drawctxt_detach(). This causes a crash because
drawctxt->active_node is not initialized.

Change-Id: I201759316cfa5dc831e1987d209c73efb97bb9ee
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>