Use serial shorthand

Marlin/src/gcode/host/M113.cpp

@@ -32,14 +32,14 @@
  *   S<seconds> Optional. Set the keepalive interval.
  */
 void GcodeSuite::M113() {
+
   if (parser.seenval('S')) {
     host_keepalive_interval = parser.value_byte();
     NOMORE(host_keepalive_interval, 60);
   }
-  else {
-    SERIAL_ECHO_START();
-    SERIAL_ECHOLNPAIR("M113 S", (unsigned long)host_keepalive_interval);
-  }
+  else
+    SERIAL_ECHO_MSG("M113 S", (uint16_t)host_keepalive_interval);
+
 }
 
 #endif // HOST_KEEPALIVE_FEATURE