sm: Fix a wrong key parameter in an exported private key file

* sm/export.c (sexp_to_kparms): Fix the computation of array[6],
which must be 'd mod (q-1)' but was 'p mod (q-1)'.
--

This bug is not serious but makes some consistency checks fail.
For example, 'openssl rsa -check' reports the following error:

$ gpgsm --out my.key --export-secret-key-raw 0xXXXXXXXX
$ openssl rsa -check -noout -inform DER -in my.key
RSA key error: dmq1 not congruent to d

--
Let me(wk) add this:

This bug was introduced with
Fixes-commit: 91056b1976
right at the start of GnuPG 2.1 in July 2010.  Before that (in 2.0) we
used gpg-protect-tool which got it right.  We probably never noticed
this because gpgsm, and maybe other tools too, fix things up during
import.

Signed-off-by: Werner Koch <wk@gnupg.org>

sm/export.c

@@ -603,7 +603,7 @@ sexp_to_kparms (gcry_sexp_t sexp)
 
   array[6] = gcry_mpi_snew (0);  /* compute d mod (p-1) */
   gcry_mpi_sub_ui (array[6], array[4], 1);
-  gcry_mpi_mod (array[6], array[3], array[6]);
+  gcry_mpi_mod (array[6], array[2], array[6]);
 
   return array;
 }