wl1271: use debugfs_remove_recursive

Documentation/filesystems/debugfs.txt:
"""
Once upon a time, debugfs users were required to remember the dentry pointer
for every debugfs file they created so that all files could be cleaned up.
We live in more civilized times now, though, and debugfs users can call:

    void debugfs_remove_recursive(struct dentry *dentry);
"""

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>