msm: kgsl: trace preempt_trigger before triggering the preemption

Updating the trace log location to prevent NULL pointer
access for adreno_dev->next_rb.
There are chances that interrupt for preemption complete
comes before driver could log this trace, and that will
lead to NULL pointer access, because while handling this
interrupt next_rb would be set to NULL.

Change-Id: I096aeccab72e36eb94608d7d96cef3b72051dd25
Signed-off-by: Pankaj Gupta <gpankaj@codeaurora.org>