fix const-ness of argument to mbedtls_ssl_conf_cert_profile

Otherwise, it's impossible to pass in a pointer to
mbedtls_x509_crt_profile_next!
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index bd88918..907bba1 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -1381,7 +1381,7 @@
  * \param profile  Profile to use
  */
 void mbedtls_ssl_conf_cert_profile( mbedtls_ssl_config *conf,
-                                    mbedtls_x509_crt_profile *profile );
+                                    const mbedtls_x509_crt_profile *profile );
 
 /**
  * \brief          Set the data required to verify peer certificate
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 14ee521..f1d2dd2 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -5372,7 +5372,7 @@
 
 #if defined(MBEDTLS_X509_CRT_PARSE_C)
 void mbedtls_ssl_conf_cert_profile( mbedtls_ssl_config *conf,
-                                    mbedtls_x509_crt_profile *profile )
+                                    const mbedtls_x509_crt_profile *profile )
 {
     conf->cert_profile = profile;
 }