Fix additional mis-spellings

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index dcb87b5..28d55dc 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -6344,7 +6344,7 @@
         MBEDTLS_SSL_DEBUG_MSG( 1, ( "There is pending outgoing data" ) );
         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
     }
-    /* Protocol must be DLTS, not TLS */
+    /* Protocol must be DTLS, not TLS */
     if( ssl->conf->transport != MBEDTLS_SSL_TRANSPORT_DATAGRAM )
     {
         MBEDTLS_SSL_DEBUG_MSG( 1, ( "Only DTLS is supported" ) );