[S390] monreader: fix use after free bug with suspend/resume

The monreader device driver doesn't set dev->driver_data to NULL after
freeing the corresponding data structure. This leads to a use after
free bug in the freeze/thaw suspend/resume functions after the device
has been opened and closed once. Fix this by clearing dev->driver_data
in the close() function.
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/char/monreader.c

@@ -357,6 +357,7 @@ static int mon_close(struct inode *inode, struct file *filp)
 	atomic_set(&monpriv->msglim_count, 0);
 	monpriv->write_index  = 0;
 	monpriv->read_index   = 0;
+	dev_set_drvdata(monreader_device, NULL);
 
 	for (i = 0; i < MON_MSGLIM; i++)
 		kfree(monpriv->msg_array[i]);