crypto: algif_skcipher - Cap recv SG list at ctx->used

commit 7cf81954 upstream.

Somewhere along the line the cap on the SG list length for receive
was lost.  This patch restores it and removes the subsequent test
which is now redundant.

Fixes: 2d97591e

 ("crypto: af_alg - consolidation of...")
Cc: <stable@vger.kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Reviewed-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>