Staging: ramzswap: Free memory when create_device is failed

If create_device is failed, it can't free gendisk and request_queue of
preceding devices. It cause memory leak.

This patch fixes it.

Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>