Use MBEDTLS_GET_UINTxx_BE macro

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/ssl_ticket.c b/library/ssl_ticket.c
index 0908982..8e7c145 100644
--- a/library/ssl_ticket.c
+++ b/library/ssl_ticket.c
@@ -444,7 +444,7 @@
         goto cleanup;
     }
 
-    enc_len = (enc_len_p[0] << 8) | enc_len_p[1];
+    enc_len = MBEDTLS_GET_UINT16_BE(enc_len_p, 0);
 
     if (len != TICKET_MIN_LEN + enc_len) {
         ret = MBEDTLS_ERR_SSL_BAD_INPUT_DATA;