drm/xe/vm: move rebind_work init earlier

In xe_vm_close_and_put() we need to be able to call
flush_work(rebind_work), however during vm creation we can call this on
the error path, before having actually set up the worker, leading to a
splat from flush_work().

It looks like we can simply move the worker init step earlier to fix
this.

Fixes: dd08ebf6 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: <stable@vger.kernel.org> # v6.8+
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20250514152424.149591-3-matthew.auld@intel.com