crypto: hisilicon/qm - flush all work before driver removed

Before removing the driver, flush inter-function communication
work, and subsequent communication work is not processed.
This prevents communication threads from accessing released memory.

Fixes: ("crypto: hisilicon/qm - enable PF and VFs communication")
Signed-off-by: Weili Qian <qianweili@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>