Fix typos prior to release

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
diff --git a/library/ssl_tls13_server.c b/library/ssl_tls13_server.c
index ce8767c..6caae89 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -634,7 +634,7 @@
 
     if( p_identity_len != identities_end || p_binder_len != binders_end )
     {
-        MBEDTLS_SSL_DEBUG_MSG( 3, ( "pre_shared_key extesion decode error" ) );
+        MBEDTLS_SSL_DEBUG_MSG( 3, ( "pre_shared_key extension decode error" ) );
         MBEDTLS_SSL_PEND_FATAL_ALERT( MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR,
                                       MBEDTLS_ERR_SSL_DECODE_ERROR );
         return( MBEDTLS_ERR_SSL_DECODE_ERROR );