[CRYPTO] scatterwalk: Restore custom sg chaining for now

Unfortunately the generic chaining hasn't been ported to all architectures
yet, and notably not s390.  So this patch restores the chainging that we've
been using previously which does work everywhere.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/crypto/hmac.c b/crypto/hmac.c
index 34c3706..a1d016a 100644
--- a/crypto/hmac.c
+++ b/crypto/hmac.c
@@ -17,6 +17,7 @@
  */
 
 #include <crypto/algapi.h>
+#include <crypto/scatterwalk.h>
 #include <linux/err.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
@@ -160,7 +161,7 @@
 
 	sg_init_table(sg1, 2);
 	sg_set_buf(sg1, ipad, bs);
-	sg_chain(sg1, 2, sg);
+	scatterwalk_sg_chain(sg1, 2, sg);
 
 	sg_init_table(sg2, 1);
 	sg_set_buf(sg2, opad, bs + ds);