fix various issues.

- comments issues
- code format style issues
- naming improvement.
- error return improvements

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ssl_tls13_keys.c b/library/ssl_tls13_keys.c
index c11ad28..3948ea6 100644
--- a/library/ssl_tls13_keys.c
+++ b/library/ssl_tls13_keys.c
@@ -1581,7 +1581,7 @@
     *psk = NULL;
 
     if( mbedtls_svc_key_id_is_null( ssl->handshake->psk_opaque ) )
-        return( MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED );
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
 
     status = psa_get_key_attributes( ssl->handshake->psk_opaque, &key_attributes );
     if( status != PSA_SUCCESS )
@@ -1609,7 +1609,7 @@
     *psk = ssl->handshake->psk;
     *psk_len = ssl->handshake->psk_len;
     if( *psk == NULL )
-        return( MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED );
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
     return( 0 );
 #endif /* !MBEDTLS_USE_PSA_CRYPTO */
 }