drm/xe/dma-buf: fix UAF with retry loop

In the Linux kernel, the following vulnerability has been resolved:

drm/xe/dma-buf: fix UAF with retry loop

Retry doesn't work here, since bo will be freed on error, leading to UAF. However, now that we do the alloc & init before the attach, we can now combine this as one unit and have the init do the alloc for us. This should make the retry safe.

Reported by Sashiko.

v2: Fix up the error unwind (CI)

(cherry picked from commit 479669418253e0f27f8cf5db01a731352ea592e7)