uacce: fix NULL pointer when unbind device

driver inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I867RA


CVE: NA

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When the user space process and 'unbind' device operations are
performed at the same time, the 'unbind' operation may be completed
before the memory is unmap(uacce_vma_close()). Since 'uacce->parent'
is set to NULL in uacce_remove(), 'pdev->driver' will trigger panic
in uacce_free_dma_buffers(). Therefore, the memory release process
is added to uacce_remove(), and uacce->mutex ensures that the memory
is released only once.

Signed-off-by: Weili Qian <qianweili@huawei.com>
Signed-off-by: JiangShui Yang <yangjiangshui@h-partners.com>