mraa-gpio: clean up on close for ain, pwm, dout

Required as nodejs will only lazily delete the node objects, and we may
race with the next user requesting the resources.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Ivan Mikhaylov <ivan.mikhaylov@siemens.com>

hardware/intel/mraa-gpio-ain.js

@@ -25,6 +25,7 @@ module.exports = function(RED) {
 
         this.on('close', function() {
             clearInterval(this.timer);
+            node.x.close();
         });
     }
     RED.nodes.registerType("mraa-gpio-ain", gpioAin);

hardware/intel/mraa-gpio-dout.js

@@ -29,6 +29,7 @@ module.exports = function(RED) {
         });
 
         this.on('close', function() {
+            node.p.close();
         });
     }
     RED.nodes.registerType("mraa-gpio-dout", gpioDout);

hardware/intel/mraa-gpio-pwm.js

@@ -21,6 +21,7 @@ module.exports = function(RED) {
 
         this.on('close', function() {
             node.p.enable(false);
+            node.p.close();
         });
     }
     RED.nodes.registerType("mraa-gpio-pwm", gpioPWM);