usbh_kbd_after_poll() typo fix

Renamed 2nd usbh_kbd_before_poll() to usbh_kbd_after_poll()

Author: jhgorse

examples/common/usbh_kbd/usbh_kbd.c

@@ -480,7 +480,7 @@ int main(void)
 
 		last = now;
 
-		usbh_kbd_before_poll();
+		usbh_kbd_after_poll();
 	}
 
 	return 0;