drm/amdgpu: fix some kerneldoc in the VM code v2

Fix two incorrect kerneldocs for the recent VM code changes.

v2: fix one more typo

Signed-off-by: Christian König <christian.koenig@amd.com>
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>