drm/vmwgfx: Add error path for xa_store in vmw_bo_add_detached_resource

The xa_store() may fail due to memory allocation failure because there
is no guarantee that the index is already used. This fix introduces new
paths to handle the error.

This patch also aligns the order of function calls by calling
vmw_bo_add_detached_resource() before ttm_prime_object_init() in order
to allow consistent error handling.

Fixes: d6667f0d ("drm/vmwgfx: Fix handling of dumb buffers")
Signed-off-by: Keisuke Nishimura <keisuke.nishimura@inria.fr>
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250225145223.34773-1-keisuke.nishimura@inria.fr