Restore behaviour of mbedtls_x509write_set_foo_name()

The documentation doesn't say you can't call these functions more than
once on the same context, and if you do it shouldn't result in a memory
leak. Historically, the call to mbedtls_asn1_free_named_data_list() in
mbedtls_x509_string_to_names() (that was removed in the previous commit)
was ensuring that. Let's restore it where it makes sense. (These are the
only 3 places calling mbedtls_x509_string_to_names() in the library.)

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>

library/x509write_crt.c

@@ -81,12 +81,14 @@ void mbedtls_x509write_crt_set_issuer_key(mbedtls_x509write_cert *ctx,
 int mbedtls_x509write_crt_set_subject_name(mbedtls_x509write_cert *ctx,
                                            const char *subject_name)
 {
+    mbedtls_asn1_free_named_data_list(&ctx->subject);
     return mbedtls_x509_string_to_names(&ctx->subject, subject_name);
 }
 
 int mbedtls_x509write_crt_set_issuer_name(mbedtls_x509write_cert *ctx,
                                           const char *issuer_name)
 {
+    mbedtls_asn1_free_named_data_list(&ctx->issuer);
     return mbedtls_x509_string_to_names(&ctx->issuer, issuer_name);
 }
 

library/x509write_csr.c

@@ -63,6 +63,7 @@ void mbedtls_x509write_csr_set_key(mbedtls_x509write_csr *ctx, mbedtls_pk_contex
 int mbedtls_x509write_csr_set_subject_name(mbedtls_x509write_csr *ctx,
                                            const char *subject_name)
 {
+    mbedtls_asn1_free_named_data_list(&ctx->subject);
     return mbedtls_x509_string_to_names(&ctx->subject, subject_name);
 }