thunderbolt: Fix memory leak in margining_port_remove()

The dentry returned by debugfs_lookup() needs to be released by calling
dput() which is missing in margining_port_remove(). Fix this by calling
debugfs_lookup_and_remove() that combines both and avoids the memory leak.

Fixes: d0f1e0c2

 ("thunderbolt: Add support for receiver lane margining")
Cc: stable@vger.kernel.org
Signed-off-by: Yaxiong Tian <tianyaxiong@kylinos.cn>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>