switch to mbedtls_pk_sigalg_t

Signed-off-by: Ben Taylor <ben.taylor@linaro.org>
diff --git a/library/x509_create.c b/library/x509_create.c
index 09ac69d..370eb9b 100644
--- a/library/x509_create.c
+++ b/library/x509_create.c
@@ -646,7 +646,7 @@
 int mbedtls_x509_write_sig(unsigned char **p, unsigned char *start,
                            const char *oid, size_t oid_len,
                            unsigned char *sig, size_t size,
-                           mbedtls_pk_type_t pk_alg)
+                           mbedtls_pk_sigalg_t pk_alg)
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     int write_null_par;
@@ -672,7 +672,7 @@
 
     // Write OID
     //
-    if (pk_alg == MBEDTLS_PK_ECDSA) {
+    if (pk_alg == MBEDTLS_PK_SIGALG_ECDSA) {
         /*
          * The AlgorithmIdentifier's parameters field must be absent for DSA/ECDSA signature
          * algorithms, see https://www.rfc-editor.org/rfc/rfc5480#page-17 and