msm: kgsl: Fix GPU busy value conversion when GMU is disabled

On A6XX, the power counters are sourced from XO clock instead
of GFX3D clock irrespective of whether GMU is enabled or
disabled.

This change makes sure that correct GPU busy conversion method
is used.

Change-Id: Idf276f7207352414204d1ee2ff95cd7757ffa5e6
Signed-off-by: Deepak Kumar <dkumar@codeaurora.org>