drm/amdkfd: err_pin_bo path leaks kfd_bo_list

Refactor userptr and pin_bo path to make it less confusing, move
err_pin_bo label up to remove mem from process_info kfd_bo_list.

Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>