msm: kgsl: Use correct offsets for VBIF counters on A4xx

VBIF counter offsets are different on A3xx and A4xx. Use the correct
offset value to access "waiting for ram" power performance counter
on both platforms.

Change-Id: I82b8ce2378742726e20186ece82ff42ff4201ce7
Signed-off-by: Vladimir Razgulin <vrazguli@codeaurora.org>