clk: msm: clock-gpu-cobalt: Use the xo_ao source for GPUCC

The root clock for all GPUCC clocks, gpucc_cxo_clk is currently
being sourced off the cxo_clk_src clock. This will not allow XO
shutdown to happen. Use the cxo_clk_src_ao instead.

CRs-Fixed: 983874
Change-Id: I7f8dd9ea28114d3d06fec3397064356b4deb6e7e
Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>