crypto: algif_hash - Fix result clobbering in recvmsg

Recently an init call was added to hash_recvmsg so as to reset
the hash state in case a sendmsg call was never made.

Unfortunately this ended up clobbering the result if the previous
sendmsg was done with a MSG_MORE flag.  This patch fixes it by
excluding that case when we make the init call.

Fixes: a8348bca

 ("algif_hash - Fix NULL hash crash with shash")
Reported-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>