msm: kgsl: Fix a wrong CSR reference during GPU power off

The replaced register does not exist and caused access control
failure. Use the correct register that is used to enable GPU
RSC driver with ID 0.

Change-Id: I0d9edb1038636c7adf8ac9619b9f009e4a1303ff
CRs-Fixed: 2017390
Signed-off-by: George Shen <sqiao@codeaurora.org>