crypto: rsa - Generate fixed-length output

Every implementation of RSA that we have naturally generates
output with leading zeroes.  The one and only user of RSA,
pkcs1pad wants to have those leading zeroes in place, in fact
because they are currently absent it has to write those zeroes
itself.

So we shouldn't be stripping leading zeroes in the first place.
In fact this patch makes rsa-generic produce output with fixed
length so that pkcs1pad does not need to do any extra work.

This patch also changes DH to use the new interface.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/crypto/rsa.c b/crypto/rsa.c
index dc692d4..4c280b6 100644
--- a/crypto/rsa.c
+++ b/crypto/rsa.c
@@ -108,7 +108,7 @@
 	if (ret)
 		goto err_free_m;
 
-	ret = mpi_write_to_sgl(c, req->dst, &req->dst_len, &sign);
+	ret = mpi_write_to_sgl(c, req->dst, req->dst_len, &sign);
 	if (ret)
 		goto err_free_m;
 
@@ -147,7 +147,7 @@
 	if (ret)
 		goto err_free_c;
 
-	ret = mpi_write_to_sgl(m, req->dst, &req->dst_len, &sign);
+	ret = mpi_write_to_sgl(m, req->dst, req->dst_len, &sign);
 	if (ret)
 		goto err_free_c;
 
@@ -185,7 +185,7 @@
 	if (ret)
 		goto err_free_m;
 
-	ret = mpi_write_to_sgl(s, req->dst, &req->dst_len, &sign);
+	ret = mpi_write_to_sgl(s, req->dst, req->dst_len, &sign);
 	if (ret)
 		goto err_free_m;
 
@@ -226,7 +226,7 @@
 	if (ret)
 		goto err_free_s;
 
-	ret = mpi_write_to_sgl(m, req->dst, &req->dst_len, &sign);
+	ret = mpi_write_to_sgl(m, req->dst, req->dst_len, &sign);
 	if (ret)
 		goto err_free_s;