When Steffen originally wrote the authenc async hash patch, he
correctly had EINPROGRESS checks in place so that we did not invoke
the original completion handler with it.

Unfortuantely I told him to remove it before the patch was applied.

As only MAY_BACKLOG request completion handlers are required to
handle EINPROGRESS completions, those checks are really needed.

This patch restores them.
Reported-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>