cifs: move to generic async completion

cifs starts an async. crypto op and waits for their completion.
Move it over to generic code doing the same.

Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
Acked-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>