drm/msm/sde: Correct the method to get the QSEED3 offset

The method used to get the QSEED3 offset is incorrect in REG_DMA
path, this change fixes the issue to get the correct QSEED3 offset.

Change-Id: Id0975752d419ab03f745f6a0236c0df03c528e0a
Signed-off-by: Ping Li <pingli@codeaurora.org>