crypto: authenc - Add EINPROGRESS check

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>