Move random function check

move to `ssl_conf_check`

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>

library/ssl_tls.c

diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 07b5100..1c8c7bd 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -3182,6 +3182,12 @@
     if( ret != 0 )
         return( ret );
 
+    if( ssl->conf->f_rng == NULL )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "no RNG provided" ) );
+        return( MBEDTLS_ERR_SSL_NO_RNG );
+    }
+
     /* Space for further checks */
 
     return( 0 );

library/ssl_tls13_client.c

diff --git a/library/ssl_tls13_client.c b/library/ssl_tls13_client.c
index 2cada0d..036c5e5 100644
--- a/library/ssl_tls13_client.c
+++ b/library/ssl_tls13_client.c
@@ -111,12 +111,6 @@
     int ret;
     size_t rand_bytes_len;
 
-    if( ssl->conf->f_rng == NULL )
-    {
-        MBEDTLS_SSL_DEBUG_MSG( 1, ( "no RNG provided" ) );
-        return( MBEDTLS_ERR_SSL_NO_RNG );
-    }
-
     rand_bytes_len = 32;
 
     if( ( ret = ssl->conf->f_rng( ssl->conf->p_rng, ssl->handshake->randbytes, rand_bytes_len ) ) != 0 )