switch to mbedtls_pk_sigalg_t

Signed-off-by: Ben Taylor <ben.taylor@linaro.org>
diff --git a/library/x509write_csr.c b/library/x509write_csr.c
index 88adf79..9040d63 100644
--- a/library/x509write_csr.c
+++ b/library/x509write_csr.c
@@ -249,7 +249,7 @@
     c2 = buf + size;
     MBEDTLS_ASN1_CHK_ADD(sig_and_oid_len,
                          mbedtls_x509_write_sig(&c2, buf + len, sig_oid, sig_oid_len,
-                                                sig, sig_len, pk_alg));
+                                                sig, sig_len, (mbedtls_pk_sigalg_t)pk_alg));
 
     /*
      * Compact the space between the CSR data and signature by moving the