wifi: iwlwifi: Fix dentry reference leak in iwl_mld_add_link_debugfs

wifi: iwlwifi: Fix dentry reference leak in iwl_mld_add_link_debugfs

The debugfs_lookup() function increases the dentry reference count.
Add missing dput() call to release the reference when the "iwlmld"
directory already exists.

Fixes: d1e879ec600f ("wifi: iwlwifi: add iwlmld sub-driver")
Cc: stable@vger.kernel.org
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Link: https://patch.msgid.link/20250902040955.2362472-1-linmq006@gmail.com
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>