Input: ibmasm - fix input initialization error path

Do not try to free device that has already been unregistered,
input_unregister_device() frees it automatically.

Spotted by Vernon Mauery <vernux@us.ibm.com>

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
diff --git a/drivers/misc/ibmasm/remote.c b/drivers/misc/ibmasm/remote.c
index 1abd0c5..0f9e3aa 100644
--- a/drivers/misc/ibmasm/remote.c
+++ b/drivers/misc/ibmasm/remote.c
@@ -270,6 +270,7 @@
 
  err_unregister_mouse_dev:
 	input_unregister_device(mouse_dev);
+	mouse_dev = NULL; /* so we don't try to free it again below */
  err_free_devices:
 	input_free_device(mouse_dev);
 	input_free_device(keybd_dev);