staging: comedi: don't release mutex too early in comedi_auto_config()

`comedi_auto_config()` uses `dev->class_dev` for logging a kernel
message after releasing `dev->mutex`.  There is an unlikely possibility
that the Comedi device `dev` will have been removed by the
`COMEDI_DEVCONFIG` ioctl() command.  Keep hold of the mutex until the
kernel message has been sent to prevent that.  The function can call
`comedi_release_hardware_device()` on error.  In that case, the mutex
must be unlocked before that.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers.c

@@ -1059,12 +1059,12 @@ int comedi_auto_config(struct device *hardware_device,
 	ret = driver->auto_attach(dev, context);
 	if (ret >= 0)
 		ret = comedi_device_postconfig(dev);
-	mutex_unlock(&dev->mutex);
 
 	if (ret < 0) {
 		dev_warn(hardware_device,
 			 "driver '%s' failed to auto-configure device.\n",
 			 driver->driver_name);
+		mutex_unlock(&dev->mutex);
 		comedi_release_hardware_device(hardware_device);
 	} else {
 		/*
@@ -1074,6 +1074,7 @@ int comedi_auto_config(struct device *hardware_device,
 		dev_info(dev->class_dev,
 			 "driver '%s' has successfully auto-configured '%s'.\n",
 			 driver->driver_name, dev->board_name);
+		mutex_unlock(&dev->mutex);
 	}
 	return ret;
 }