Fix warnings reported by kernel test bot/smatch

smatch warnings:
drivers/gpu/drm/amd/amdgpu/amdgpu_xcp.c:65 amdgpu_xcp_run_transition()
error: buffer overflow 'xcp_mgr->xcp' 8 <= 8
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <error27@gmail.com>
Link: https://lore.kernel.org/r/202305231453.I0bXngYn-lkp@intel.com/Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>