drm/i915/gvt: destroy the allocated idr on vgpu creating failures

Once idr_alloc gets called data is allocated within the idr list, if
any error occurs afterwards, we should undo that by idr_remove on the
error path.

Signed-off-by: Jike Song <jike.song@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>