drm/amdgpu: fix a few compiler warnings

1. make function mmhub_v1_7_setup_vm_pt_regs static
2. indent a if statement

Signed-off-by: Oak Zeng <Oak.Zeng@amd.com>
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>