accel/amdxdna: Fix use-after-free in amdxdna_gem_dmabuf_mmap()

accel/amdxdna: Fix use-after-free in amdxdna_gem_dmabuf_mmap()

When vm_insert_pages() fails, the error path calls vma->vm_ops->close(vma)
which internally calls drm_gem_vm_close() → drm_gem_object_put(),
releasing the GEM object reference acquired at the start of the function.
However, the close_vma label then falls through to put_obj, which calls
drm_gem_object_put() a second time on the same object.

If the first put releases the last reference, the object is freed and the
second put accesses freed memory, causing a use-after-free.

Fix by returning directly from close_vma instead of falling through to
put_obj, since the close handler already performs all necessary cleanup
including the object put.

Cc: stable@vger.kernel.org
Fixes: e486147c912f ("accel/amdxdna: Add BO import and export")
Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
Reviewed-by: Lizhi Hou <lizhi.hou@amd.com>
Signed-off-by: Lizhi Hou <lizhi.hou@amd.com>
Link: https://patch.msgid.link/20260625113239.49764-1-vulab@iscas.ac.cn