crypto: null - Switch to shash

This patch changes digest_null to the new shash interface.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/crypto/Kconfig b/crypto/Kconfig
index aede802..359a7c2 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -102,6 +102,7 @@
 	tristate "Null algorithms"
 	select CRYPTO_ALGAPI
 	select CRYPTO_BLKCIPHER
+	select CRYPTO_HASH
 	help
 	  These are 'Null' algorithms, used by IPsec, which do nothing.