[sftp] reformat to 4 space indentation

Summary:
while that generates history noise it's also much easier on the eyes and
something @asn wants to happen.

so, here we are

Test Plan: builds

Reviewers: asn, ngraham, apol

Reviewed By: ngraham, apol

Subscribers: asn, kde-frameworks-devel, kfm-devel, broulik

Tags: #dolphin, #frameworks

Differential Revision: https://phabricator.kde.org/D16385